A
solid-state drive sometimes called a
solid-state disk or
electronic disk, is a
data storage devicethumb|200px|right|A reel-to-reel tape recorder .The magnetic tape is a data storage medium. The recorder is data storage equipment using a portable medium to store the data....
that uses solid-state
memoryComputer data storage, often called storage or memory, refers to computer components and recording media that retain digital data. Data storage is one of the core functions and fundamental components of computers....
to store
persistent dataPersistence in computer science refers to the characteristic of state that outlives the process that created it. Without this capability, state would only exist in RAM, and would be lost when this RAM loses power, such as a computer shutdown....
with the intention of providing access in the same manner of a traditional block i/o hard disk drive. SSDs are distinguished from traditional magnetic disks such as hard disk drives (HDDs) or
floppy diskA floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
, which are electromechanical devices containing spinning
disksDisk storage or disc storage is a general category of storage mechanisms, in which data are digitally recorded by various electronic, magnetic, optical, or mechanical methods on a surface layer deposited of one or more planar, round and rotating disks...
and movable
read/write headsDisk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...
. In contrast, SSDs use
microchipAn integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s that retain data in non-volatile memory chips and contain no
moving partsThe moving parts of a machine are those parts of it that move. Machines comprise both moving and fixed parts. The moving parts have controlled and constrained motions....
. Compared to electromechanical HDDs, SSDs are typically less susceptible to physical shock, are silent, have lower
access timeAccess time is the time delay or latency between a request to an electronic system, and the access being completed or the requested data returned....
and
latencyLatency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...
, but are more expensive per
gigabyteThe gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...
(GB). SSDs use the same interface as hard disk drives, thus easily replacing them in most applications.
, most SSDs use NAND-based flash memory, which retains memory even without power. SSDs using volatile
random-access memoryRandom access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...
(RAM) also exist for situations that require even faster access, but do not necessarily need data
persistencePersistence in computer science refers to the characteristic of state that outlives the process that created it. Without this capability, state would only exist in RAM, and would be lost when this RAM loses power, such as a computer shutdown....
after power loss, or use external power or batteries to maintain the data after power is removed.
A
hybrid driveA Hybrid Drive, Hybrid Hard Drive , or Hybrid Hard Disk Drive is a type of large-buffer computer hard disk drive. It is different from standard hard drives in that it integrates a cache using non-volatile memory or even a small solid-state drive...
combines the features of an HDD and an SSD into one unit, containing a large HDD and a smaller SSD cache to improve performance of frequently accessed files. These can offer near-SSD performance in most applications (such as system startup and loading applications) at a lower price than an SSD. These are not suitable for data-intensive work, nor do they offer the other advantages of SSDs.
Early SSDs using RAM and similar technology
The origins of SSDs came from the 1950s using two similar technologies,
magnetic core memoryMagnetic-core memory was the predominant form of random-access computer memory for 20 years . It uses tiny magnetic toroids , the cores, through which wires are threaded to write and read information. Each core represents one bit of information...
and card capacitor read-only store (CCROS). These auxiliary memory units, as they were called at the time, emerged during the era of
vacuum tubeIn electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
computers. But with the introduction of cheaper
drum storage unitsDrum memory is a magnetic data storage device and was an early form of computer memory widely used in the 1950s and into the 1960s, invented by Gustav Tauschek in 1932 in Austria....
, their use was discontinued.
Later, in the 1970s and 1980s, SSDs were implemented in semiconductor memory for early supercomputers of
IBMInternational Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
,
AmdahlAmdahl Corporation is an information technology company which specializes in IBM mainframe-compatible computer products. Founded in 1970 by Dr. Gene Amdahl, a former IBM employee, it has been a wholly owned subsidiary of Fujitsu since 1997...
and
CrayCray Inc. is an American supercomputer manufacturer based in Seattle, Washington. The company's predecessor, Cray Research, Inc. , was founded in 1972 by computer designer Seymour Cray. Seymour Cray went on to form the spin-off Cray Computer Corporation , in 1989, which went bankrupt in 1995,...
; however, the prohibitively high price of the built-to-order SSDs made them quite seldom used. In the late 1970s, General Instruments produced an electrically alterable ROM (EAROM) which operated somewhat like the later NAND flash memory, but the inability to achieve a 10-year life was not practical and many companies abandoned the technology. In 1976
DataramDataram Corporation is an international manufacturer of computer memory, storage, and software products, founded in 1967 as a supplier of original equipment memory to Digital Equipment Corporation.-Company overview:...
started selling a product called
BULK CORE providing up to 2MB of solid state storage compatible with
DECDigital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
and
Data GeneralData General was one of the first minicomputer firms from the late 1960s. Three of the four founders were former employees of Digital Equipment Corporation. Their first product, the Data General Nova, was a 16-bit minicomputer...
computers.
Texas Memory SystemsTexas Memory Systems, Inc. is a privately held American corporation that designs and manufacturers solid-state disks and digital signal processors . TMS was founded in 1978 and that same year introduced their first solid-state drive, followed by their first digital signal processor...
introduced a 16
kilobyteThe kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
(KB) RAM solid-state drive in 1978 to be used by oil companies for
seismic dataReflection seismology is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismic source of energy, such as dynamite/Tovex, a specialized air gun or a...
acquisition. The following year, StorageTek developed the first modern type of solid-state drive.
The
Sharp PC-5000The Sharp PC-5000 was a pioneering laptop computer, announced by Sharp Corporation of Japan in 1983. Like the GRiD Compass, which preceded it, and its contemporary the Gavilan SC, it employed a clamshell design in which the display closes over the keyboard....
, introduced in 1983, used 128 kilobyte solid-state storage cartridges, containing
bubble memoryBubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles or domains, each storing one bit of data...
. In 1984 Tallgrass Technologies Corporation had a tape back up unit of 40 MB with a solid state 20 MB unit built in. The 20 MB unit could be used instead of a hard drive. In September 1986, Santa Clara Systems introduced BatRam, 4
megabyteThe megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
(MB) mass storage system expandable to 20 MB using 4 MB memory modules. The package included a rechargeable battery to preserve the memory chip contents when the array was not powered. 1987 saw the entry of
EMC CorporationEMC Corporation , a Financial Times Global 500, Fortune 500 and S&P 500 company, develops, delivers and supports information infrastructure and virtual infrastructure hardware, software, and services. EMC is headquartered in Hopkinton, Massachusetts, USA.Former Intel executive Richard Egan and his...
into the SSD market, with drives introduced for the mini-computer market. However, by 1993 EMC had exited the SSD market.
Software-based
RAM DiskA RAM disk or RAM drive is a block of RAM that a computer's software is treating as if the memory were a disk drive...
s are still used today because they are an
order of magnitudeAn order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. In its most common usage, the amount being scaled is 10 and the scale is the exponent being applied to this amount...
faster than the fastest SSD, but they consume CPU resources and cost much more on a per GB basis.
Flash-based SSDs
In 1994,
STEC, Inc.STEC, Inc. is a multinational company and a leader in enterprise solid-state drive .The company is headquartered in Santa Ana, California...
bought Cirrus Logic’s flash controller operation, allowing the company to enter the flash memory business for consumer electronic devices.
In 1995,
M-SystemsM-Systems Ltd., was a Nasdaq-listed Israeli producer of Flash memory storage products founded in 1989 by Dov Moran and based in Kfar Sava, Israel. They were best known for developing and patenting the first flash drive, marketed in 1995 as DiskOnChip, and the first USB flash drive, marketed in...
introduced flash-based solid-state drives. They had the advantage of not requiring batteries to maintain the data in the memory (required by the prior volatile memory systems), but were not as fast as the DRAM-based solutions. Since then, SSDs have been used successfully as HDD replacements by the military and aerospace industries, as well as for other mission-critical applications. These applications require the exceptional mean time between failures (MTBF) rates that solid-state drives achieve, by virtue of their ability to withstand extreme shock, vibration and temperature ranges.
BiTMICRO made a number of introductions and announcements in 1999 around flash-based SSDs including an 18 GB 3.5 in SSD. Fusion-io announced a PCIe-based SSD with 100,000
input/output operations per secondIOPS is a common performance measurement used to benchmark computer storage devices like hard disk drives , solid state drives , and storage area networks...
(IOPS) of performance in a single card with capacities up to 320 gigabytes in 2007. At Cebit 2009, OCZ demonstrated a 1
terabyteThe terabyte is a multiple of the unit byte for digital information. The prefix tera means 1012 in the International System of Units , and therefore 1 terabyte is , or 1 trillion bytes, or 1000 gigabytes. 1 terabyte in binary prefixes is 0.9095 tebibytes, or 931.32 gibibytes...
(TB) flash SSD using a PCI Express ×8 interface. It achieves a maximum write speed of 654 megabytes per second (MB/s) and maximum read speed of 712 MB/s. In December 2009,
Micron TechnologyMicron Technology, Inc. is an American multinational corporation based in Boise, Idaho, USA, best known for producing many forms of semiconductor devices. This includes DRAM, SDRAM, flash memory, SSD and CMOS image sensing chips. Consumers may be more familiar with its consumer brand Crucial...
announced the world's first SSD using a 6 gigabits per second (Gbit/s) or 600 (MB/s)
SATASata is a traditional dish from the Malaysian state of Terengganu, consisting of spiced fish meat wrapped in banana leaves and cooked on a grill.It is a type of Malaysian fish cake, or otak-otak...
interface.
Enterprise flash drives
Enterprise flash drives (EFDs) are designed for applications requiring high I/O performance (
IOPSIOPS is a common performance measurement used to benchmark computer storage devices like hard disk drives , solid state drives , and storage area networks...
), reliability, and energy efficiency. In most cases an EFD is an SSD with a higher set of specifications compared to SSDs that would typically be used in notebook computers. The term was first used by EMC in January 2008, to help them identify SSD manufacturers who would provide products meeting these higher standards. There are no standards bodies who control the definition of EFDs, so any SSD manufacturer may claim to produce EFDs when they may not actually meet the requirements. Likewise there may be other SSD manufacturers that meet the EFD requirements without being called EFDs.
Architecture and function
The key components of an SSD are the controller and the memory to store the data. The primary memory component in an SSD had been
DRAMDram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...
volatile memoryVolatile memory, also known as volatile storage, is computer memory that requires power to maintain the stored information, unlike non-volatile memory which does not require a maintained power supply...
since they were first developed, but since 2009 it is more commonly NAND flash
non-volatile memoryNon-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...
. Other components play a less significant role in the operation of the SSD and vary between manufacturers.
Controller
Every SSD includes a
controllerA flash memory controller manages the data stored on flash memory and communicates with a computer or electronic device. Flash memory controllers can be designed for operating in low duty-cycle environments like SD cards, CompactFlash cards, or other similar media for use in digital cameras, PDAs,...
that incorporates the electronics that bridge the NAND memory components to the host
computerA computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
. The controller is an embedded processor that executes firmware-level code and is one of the most important factors of SSD performance. Some of the functions performed by the controller include:
- Error correction (ECC)
- Wear leveling
Wear leveling is a technique for prolonging the service life of some kinds of erasable computer storage media, such as Flash memory used in solid-state drives and USB Flash drives...
- Bad block
Bad Sector is an ambient/noise project formed in 1992 in Tuscany, Italy by Massimo Magrini. While working at the Computer Art Lab of ISTI in Pisa , he developed original gesture interfaces that he uses in live performances: 'Aerial Painting Hand' , 'UV-Stick' Bad Sector is an ambient/noise...
mapping
- Read scrubbing
Memory scrubbing is the process of detecting and correcting bit errors in computer memory by using error-detecting codes like ECC.-Motivation for scrubbing:...
and read disturb management
- Read and write caching
In computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...
- Garbage collection
- Encryption
In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...
The performance of the SSD can scale with the number of parallel NAND flash chips used in the device. A single NAND chip is relatively slow, due to narrow (8/16 bit) asynchronous IO interface, and additional high latency of basic IO operations (typical for SLC NAND, ~25
μsA microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
to fetch a 4K page from the array to the IO buffer on a read, ~250 μs to commit a 4K page from the IO buffer to the array on a write, ~2 ms to erase a 256 kiB block). When multiple NAND devices operate in parallel inside an SSD, the bandwidth scales, and the high latencies can be hidden, as long as enough outstanding operations are pending and the load is evenly distributed between devices. Micron and Intel initially made faster SSDs by implementing
data stripingIn computer data storage, data striping is the technique of segmenting logically sequential data, such as a file, in a way that accesses of sequential segments are made to different physical storage devices. Striping is useful when a processing device requests access to data more quickly than a...
(similar to
RAIDRAID is a storage technology that combines multiple disk drive components into a logical unit...
0) and interleaving in their architecture. This enabled the creation of ultra-fast SSDs with 250 MB/s effective read/write speeds with the SATA 3 Gb/s interface in 2009. Two years later and continuing to leverage this parallel flash connectivity, SandForce released consumer-grade SATA 6 Gb/s SSD controllers which support 500 MB/s read/write speeds.
Flash memory-based
Most SSD manufacturers use
non-volatile NAND flash memoryFlash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
in the construction of their SSDs because of the lower cost compared to
DRAMDram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...
. and the ability to retain the data without a constant power supply, ensuring data persistence through sudden power outages. Flash memory SSDs are slower than DRAM solutions, and some early designs were even slower than HDDs after continued use. This problem was resolved by controllers that came out in 2009 and later.
Flash memory-based solutions are typically packaged in standard disk drive form factors (1.8-, 2.5-, and 3.5-inch), or smaller unique and compact layouts because of the compact memory.
Lower priced drives usually use
multi-level cellIn electronics, a multi-level cell is a memory element capable of storing more than a single bit of information.MLC NAND flash is a flash memory technology using multiple levels per cell to allow more bits to be stored using the same number of transistors...
(MLC) flash memory, which is slower and less reliable than single-level cell (SLC) flash memory. This can be mitigated or even reversed by the internal design structure of the SSD, such as interleaving, changes to writing algorithms, and higher over-provisioning (more excess capacity) with which the wear-leveling algorithms can work.
DRAM-based
SSDs based on volatile memory such as DRAM are characterized by ultrafast data access, generally less than 10
microsecondA microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
s, and are used primarily to accelerate applications that would otherwise be held back by the latency of flash SSDs or traditional HDDs. DRAM-based SSDs usually incorporate either an internal battery or an external AC/DC adapter and
backupIn information technology, a backup or the process of backing up is making copies of data which may be used to restore the original after a data loss event. The verb form is back up in two words, whereas the noun is backup....
storage systems to ensure data persistence while no power is being supplied to the drive from external sources. If power is lost, the battery provides power while all information is copied from random access memory (RAM) to back-up storage. When the power is restored, the information is copied back to the RAM from the back-up storage, and the SSD resumes normal operation (similar to the
hibernateHibernation in computing is powering down a computer while retaining its state.Upon hibernation, the computer saves the contents of its random access memory to a hard disk or other non-volatile storage...
function used in modern operating systems).
SSDs of this type are usually fitted with DRAM modules of the same type used in regular PCs and servers, which can be swapped out and replaced by larger modules.
A
remote, indirect memory-access disk (RIndMA Disk) uses a secondary computer with a fast network or (direct)
InfinibandInfiniBand is a switched fabric communications link used in high-performance computing and enterprise data centers. Its features include high throughput, low latency, quality of service and failover, and it is designed to be scalable...
connection to act like a RAM-based SSD, but the new faster flash memory based SSDs already available in 2009 are making this option not as cost effective.
Cache or buffer
A flash-based SSD typically uses a small amount of DRAM as a cache, similar to the cache in Hard disk drives. A directory of block placement and wear leveling data is also kept in the cache while the drive is operating. Data is not permanently stored in the cache. One SSD controller manufacturer,
SandForceSandForce is an American "fabless" semiconductor company based in Milpitas, California, that designs and manufactures flash memory controllers for solid-state drives . On October 26th 2011 it was acquired by LSI Corporation....
, does not use an external DRAM cache on their designs, but still achieve very high performance. Eliminating the external DRAM enables a smaller footprint for the other flash memory components in order to build even smaller SSDs.
Battery or super capacitor
Another component in higher performing SSDs is a capacitor or some form of battery. These are necessary to maintain data integrity such that the data in the cache can be flushed to the drive when power is dropped; some may even hold power long enough to maintain data in the cache until power is resumed. In the case of MLC flash memory, a problem called
lower page corruption can occur when MLC flash memory loses power while programming an upper page. The result is data written previously and presumed safe can be corrupted if the memory is not supported by a super capacitor in the event of a sudden power loss. This problem does not exist with SLC flash memory.
Host interface
The host interface is not specifically a component of the SSD, but it is a key part of the drive. The interface is usually incorporated into the controller discussed above. The interface is generally one of the interfaces found in HDDs. They include:
- Serial ATA
Serial ATA is a computer bus interface for connecting host bus adapters to mass storage devices such as hard disk drives and optical drives...
- Serial attached SCSI
Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,...
(generally found on serversIn the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
)
- PCI Express
PCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...
- Fibre Channel
Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
(almost exclusively found on servers)
- USB
- Parallel ATA
Parallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...
(IDEParallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...
) interface (mostly replaced by SATA)
- (Parallel) SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
(generally found on servers; mostly replaced by SAS; last SCSI-based SSD introduced in 2004)
Form factor
The size and shape of any device is largely driven by the size and shape of the components used to make that device. Traditional HDDs and optical drives are designed around the rotating platter or
optical discIn computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...
along with the spindle motor inside. If an SSD is made up of various interconnected integrated circuits (ICs) and an interface connector, then its shape could be virtually anything imaginable because it is no longer limited to the shape of rotating media drives. Some solid state storage solutions come in a larger chassis that may even be a rack-mount form factor with numerous SSDs inside. They would all connect to a common bus inside the chassis and connect outside the box with a single connector.
Standard HDD form factors
The benefit of using a current HDD form factor would be to take advantage of the extensive infrastructure already in place to mount and connect the drives to the host system. These traditional form factors are known by the size of the rotating media, e.g., 5.25", 3.5", 2.5", 1.8", not by the dimensions of the drive casing.
Box form factors
Many of the DRAM-based solutions use a box that is often designed to fit in a rack-mount system. The number of DRAM components required to get sufficient capacity to store the data along with the backup power supplies requires a larger space than traditional HDD form factors.
Bare-board form factors
Form factors which were more common to memory modules are now being used by SSDs to take advantage of their flexibility in laying out the components. Some of these include
PCIePCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...
, mini PCIe, mini-DIMM, MO-297, and many more. The SATADIMM from Viking Modular uses an empty DDR3 DIMM slot on the motherboard to provide power to the drive with a separate SATA connector to provide the data connection back to the computer. The result is an easy to install SSD with a capacity equal to drives that typically take a full 2.5 in expansion slot. At least one manufacturer, InnoDisk, is producing a drive that sits directly on the SATA connector on the motherboard without any other support or mechanical mount. Some SSDs are based on the PCIe form factor and connect both the data interface and power through the PCIe connector to the host. These drives can use either direct PCIe flash controllers or a PCIe-to-SATA bridge device which then connects to SATA flash controller(s).
Ball grid array form factors
In the early 2000s, a few companies introduced SSDs in
Ball Grid ArrayA ball grid array is a type of surface-mount packaging used for integrated circuits.- Description :The BGA is descended from the pin grid array , which is a package with one face covered with pins in a grid pattern. These pins conduct electrical signals from the integrated circuit to the printed...
(BGA) form factors, such as M-Systems’ (now
SanDiskSanDisk Corporation is an American multinational corporation that designs, develops and manufactures data storage solutions in a range of form factors using the flash memory, controller and firmware technologies. It was founded in 1988 by Dr. Eli Harari and Sanjay Mehrotra, non-volatile memory...
) DiskOnChip and
Silicon Storage TechnologySilicon Storage Technology, Inc. is a Sunnyvale, California, USA, technology company producing non-volatile memory devices and related products.It was founded by Bing Yeh in 1989....
’s NANDrive (now produced by
Greenliant SystemsGreenliant Systems is a manufacturer of flash memory, solid-state storage and controller semiconductors for embedded system, data center and mobile products. Greenliant was founded in 2010, when former Silicon Storage Technology CEO Bing Yeh acquired several flash memory assets from the company...
), and
MemorightMemoright is a Taiwan based storage products house founded in March 2006.It produced a 2.5inch SSD with a claimed read/write speed of 100mb/s, the fastest SSD available at the time....
's M1000 for use in embedded systems. The main benefits of BGA SSDs are their low power consumption, small chip package size to fit into compact subsystems, and that they can be soldered directly onto a system motherboard to reduce adverse effects from vibration and shock.
Comparison of SSD with hard disk drives
Making a comparison between SSDs and ordinary (spinning) HDDs is difficult. Traditional HDD
benchmarksIn computing, a benchmark is the act of running a computer program, a set of programs, or other operations, in order to assess the relative performance of an object, normally by running a number of standard tests and trials against it...
are focused on finding the performance aspects where they are weak, such as rotational latency time and seek time. As SSDs do not spin, or seek, they may show huge superiority in such tests. However, SSDs have challenges with mixed reads and writes, and their performance may degrade over time. SSD testing must start from the (in use) full disk, as the new and empty (fresh out of the box) disk may have much better write performance than it would show after only weeks of use.
Comparisons reflect typical characteristics, and may not hold for a specific device.
| Attribute or characteristic |
Solid-state drive |
Hard disk drive |
| Spin-up Spin-up refers to the process of a traditional hard disk drive accelerating its platters from a stopped state to an operational speed. The period of time taken by the drive to perform this process is referred to as its spin-up time, the average of which is a S.M.A.R.T. attribute. The required...
time |
Almost Instantaneous; nothing mechanical to "spin up". May need a few milliseconds to come out of an automatic power-saving mode. |
May take several seconds. With a large number of drives, spin-up may need to be staggered to limit total power drawn. |
| Random access In computer science, random access is the ability to access an element at an arbitrary position in a sequence in equal time, independent of sequence size. The position is arbitrary in the sense that it is unpredictable, thus the use of the term "random" in "random access"...
time |
About 0.1 ms - many times faster than HDDs because data is accessed directly from the flash memory |
Ranges from 5–10 ms due to the need to move the heads and wait for the data to rotate under the read/write head Disk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...
|
| Read latency time |
Generally low because the data can be read directly from any location; In applications where hard disk seeks are the limiting factor, this results in faster boot and application launch times (see Amdahl's law Amdahl's law, also known as Amdahl's argument, is named after computer architect Gene Amdahl, and is used to find the maximum expected improvement to an overall system when only part of the system is improved...
). |
Generally high since the mechanical components require additional time to get aligned |
| Consistent read performance |
Read performance does not change based on where data is stored on an SSD |
If data is written in a fragmented way, reading back the data will have varying response times |
DefragmentationIn the maintenance of file systems, defragmentation is a process that reduces the amount of fragmentation. It does this by physically organizing the contents of the mass storage device used to store files into the smallest number of contiguous regions . It also attempts to create larger regions of...
|
SSDs do not benefit from defragmentation because there is little benefit to reading data sequentially (beyond typical FS block sizes) and any defragmentation process adds additional writes on the NAND flash that already have a limited cycle life. |
HDDs may require defragmentation after continued operations or erasing and writing data, especially involving large files . |
AcousticAcoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...
levels |
SSDs have no moving parts and make no sound |
HDDs have moving parts (heads, spindle motor) and have varying levels of sound depending upon model |
Mechanical reliabilityReliability engineering is an engineering field, that deals with the study, evaluation, and life-cycle management of reliability: the ability of a system or component to perform its required functions under stated conditions for a specified period of time. It is often measured as a probability of...
|
A lack of moving parts virtually eliminates mechanical breakdowns |
HDDs have many moving parts that are all subject to failure over time |
| Susceptibility to environmental factors |
No flying heads or rotating platters to fail as a result of shock, altitude, or vibration |
The flying heads and rotating platters are generally susceptible to shock, altitude, and vibration |
| Magnetic Magnetic storage and magnetic recording are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using...
susceptibility |
No impact on flash memory |
Magnets or magnetic surges can alter data on the media |
| Weight and size |
The weight of flash memory and the circuit board material are very light compared to HDDs |
Higher performing HDDs require heavier components than laptop HDDs (which are light, but not as light as SSDs) |
| Parallel operation |
Some flash controllers can have multiple flash chips reading and writing different data simultaneously |
HDDs have multiple heads (one per platter) but they are connected, and share one positioning motor. |
| Write longevity |
Flash-based SSDs have a limited number of writes (1-5 million or more) over the life of the drive. Software controllers manage this limitation in such a way that drives can last for many decades before failure. SSDs based on DRAM do not have a limited number of writes. |
Magnetic media do not have a similar limited number of writes but are susceptible to eventual mechanical failure. |
| Software encryption limitations |
NAND flash memory cannot be overwritten, but has to be rewritten to previously erased blocks. If a software encryption In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...
program encrypts data already on the SSD, the overwritten data is still unsecured, unencrypted, and accessible (drive-based hardware encryption does not have this problem). Also data cannot be securely erased by overwriting the original file without special "Secure Erase" procedures built into the drive. |
HDDs can overwrite data directly on the drive in any particular sector. |
| Cost per capacity |
, NAND flash SSDs cost about (US)$.90–2.00 per GB |
, HDDs cost about (US)$0.05/GB for 3.5 in and $0.10/GB for 2.5 in drives |
| Storage capacity |
, SSDs come in different sizes up to 2TB but are typically not larger than 64-256GB, due to their high cost per GB. |
, HDDs are typically 500GB-1TB but drives as large as 2 or 3 TB are also available. |
| Read/write performance symmetry |
Less expensive SSDs typically have write speeds significantly lower than their read speeds. Higher performing SSDs have a balanced read and write speed. |
HDDs generally have slightly lower write speeds than their read speeds. |
| Free block availability and TRIM Trim may refer to:* Cutting small pieces off something** Book trimming, a stage of the publishing process** Editing*** Editing a posting style in online discourse** Pruning, trimming as a form of pruning often used on trees-Places:...
|
SSD write performance is significantly impacted by the availability of free, programmable blocks. Previously written data blocks that are no longer in use can be reclaimed by TRIM; however, even with TRIM, fewer free, programmable blocks translates into reduced performance. |
HDDs are not affected by free blocks or the operation (or lack) of the TRIM command |
| Power consumption |
High performance flash-based SSDs generally require 1/2 to 1/3 the power of HDDs; High performance DRAM SSDs generally require as much power as HDDs and consume power when the rest of the system is shut down. |
High performance HDDs generally require between 12-18 watts; drives designed for notebook computers are typically 2 watts. |
Comparison of SSD with memory cards
While it is true that both memory cards and most SSDs use flash memory, they serve very different markets and purposes. Each has a number of different attributes which are optimized and adjusted to best meet the needs of particular users. Some of these characteristics include power consumption, performance, size, and reliability.
SSDs were originally designed for use in a computer system. The first units were intended to replace or augment hard disk drives, so the operating system recognized them as a hard drive. Originally, solid state drives were even shaped and mounted in the computer like hard drives. Later SSDs became smaller and more compact, eventually developing their own unique form factors. The SSD was designed to be installed one time inside the computer and only have it removed when servicing or upgrading it.
In contrast, memory cards like
CompactFlashCompactFlash is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994...
(CF),
Secure DigitalSecure Digital is a non-volatile memory card format developed by the SD Card Association for use in portable devices. The SD technology is used by more than 400 brands across dozens of product categories and more than 8,000 models, and is considered the de-facto industry standard.Secure Digital...
(SD), Memory Stick, and xD-Picture Card were all originally designed for digital cameras and later found their way into cell phones, gaming devices, and GPS units. Nearly all memory cards are smaller in size than SSDs and they were engineered to be inserted and removed repeatedly. There are adapters which enable some memory cards like the CF card to interface to a computer as an SSD, but they are not intended to be the primary storage device in the computer. The typical CF card interface is generally 3-4 times slower than is available on SSDs.
Cost and capacity
The technological trend of
2 yearMoore's law describes a long-term trend in the history of computing hardware: the number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years....
50% decline in costs is no longer possible in NAND flash as it approaches its terminal node. Instead NAND makers anticipate more modest cost declines in the period 2011-2015. Capacities in client SSDs are typically dictated by cost concerns rather than technical limitations of NAND storage.
Availability
Solid-state drive (SSD) technology has been marketed to the military and niche industrial markets since the mid-1990s..
Along with the emerging enterprise market, SSDs have been appearing in ultra-mobile PCs and a few lightweight laptop systems, adding significantly to the price of the laptop, depending on the capacity, form factor and transfer speeds. , some manufacturers have begun shipping affordable, fast, energy-efficient drives priced at $350 to computer manufacturers. For low-end applications, a USB flash drive may be obtainable for anywhere from $10 to $100 or so, depending on capacity; alternatively, a
CompactFlashCompactFlash is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994...
card may be paired with a CF-to-IDE or CF-to-SATA converter at a similar cost. Either of these requires that write-cycle endurance issues be managed, either by refraining from storing frequently written files on the drive or by using a
flash file systemA flash file system is a file system designed for storing files on flash memory devices. These are becoming more prevalent as the number of mobile devices is increasing, the cost per memory size decreases, and the capacity of flash memories increases....
. Standard CompactFlash cards usually have write speeds of 7 to 15 MB/s while the more expensive upmarket cards claim speeds of up to 60 MB/s.
One of the first mainstream releases of SSD was the
XO LaptopThe XO-1, previously known as the $100 Laptop, Children's Machine, and 2B1, is an inexpensive subnotebook computer intended to be distributed to children in developing countries around the world, to provide them with access to knowledge, and opportunities to "explore, experiment and express...
, built as part of the One Laptop Per Child project. Mass production of these computers, built for children in developing countries, began in December 2007. These machines use 1,024 MiB SLC NAND flash as primary storage which is considered more suitable for the harsher than normal conditions in which they are expected to be used.
DellDell, Inc. is an American multinational information technology corporation based in 1 Dell Way, Round Rock, Texas, United States, that develops, sells and supports computers and related products and services. Bearing the name of its founder, Michael Dell, the company is one of the largest...
began shipping ultra-portable laptops with SanDisk SSDs on April 26, 2007.
AsusASUSTeK Computer Incorporated is a multinational computer technology and consumer electronics product manufacturer headquartered in Taipei, Taiwan. Its product range includes motherboards, desktops, laptops, monitors, tablet PCs, servers and mobile phones...
released the
Eee PCThe Asus Eee PC is a subnotebook/netbook computer line from ASUSTeK Computer Incorporated, and a part of the Asus Eee product family. At the time of its introduction in late 2007, it was noted for its combination of a light weight, Linux operating system, solid-state drive , and relatively low cost...
subnotebookA subnotebook is a class of laptop computers that are smaller and lighter than a typical laptop....
on October 16, 2007, and after a successful commercial start in 2007, it was expected to ship several million PCs in 2008, with 2, 4 or 8 gigabytes of flash memory. On January 31, 2008, Apple Inc. released the
MacBook AirThe MacBook Air family is a line of Apple ultraportable Macintosh notebook computers.The first-generation MacBook Air was a 13.3"-only model, previously promoted as the World's Thinnest Notebook, introduced at the Macworld Conference & Expo on January 15, 2008. It featured a custom Intel Merom CPU...
, a thin laptop with optional 64 GB SSD. The Apple Store cost was $999 more for this option, as compared to that of an 80 GB 4200 RPM hard disk drive. Another option, the Lenovo
ThinkPadThinkPad is line of laptop computers originally sold by IBM but now produced by Lenovo. They are known for their boxy black design, which was modeled after a traditional Japanese lunchbox...
X300 with a 64 gigabyte SSD, was announced by Lenovo in February 2008, and is, , available to consumers in some countries. On August 26, 2008, Lenovo released ThinkPad X301 with 128GB SSD option which adds approximately $200 US.
In 2008, low end netbooks appeared with SSDs. In 2009, SSDs began to appear in laptops.
On January 14, 2008,
EMCEMC Corporation , a Financial Times Global 500, Fortune 500 and S&P 500 company, develops, delivers and supports information infrastructure and virtual infrastructure hardware, software, and services. EMC is headquartered in Hopkinton, Massachusetts, USA.Former Intel executive Richard Egan and his...
became the first enterprise storage vendor to ship flash-based SSDs into its product portfolio.
In late 2008,
SunSun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
released the
Sun Storage 7000 Unified Storage Systems (codenamed Amber Road), which use both solid state drives and conventional hard drives to take advantage of the speed offered by SSDs and the economy and capacity offered by conventional hard disks.
DellDell, Inc. is an American multinational information technology corporation based in 1 Dell Way, Round Rock, Texas, United States, that develops, sells and supports computers and related products and services. Bearing the name of its founder, Michael Dell, the company is one of the largest...
began to offer optional 256 GB solid state drives on select notebook models in January 2009.
In May 2009, Toshiba launched a laptop with a 512 GB SSD.
, Apple's
MacBook AirThe MacBook Air family is a line of Apple ultraportable Macintosh notebook computers.The first-generation MacBook Air was a 13.3"-only model, previously promoted as the World's Thinnest Notebook, introduced at the Macworld Conference & Expo on January 15, 2008. It featured a custom Intel Merom CPU...
line carries solid state drives as standard.
In December 2010,
OCZOCZ Technology is a manufacturer of computer hardware based in San Jose, California, USA. Since entering the memory market in 2002, OCZ has targeted its products primarily at the computer hardware enthusiast market, first producing performance DDR RAM, Video Cards, USB drives, and various Cooling...
RevoDrive X2 PCIe SSD was available in 100GB to 960GB capacities delivering speeds over 740MB/s sequential speeds and random small file writes up to 120,000 IOPS.
In November 2010, Fusion-io released its highest performing SSD drive named ioDrive Octal utilising PCI-Express x16 Gen 2.0 interface with storage space of 5.12TB, read speed of 6.0GB/s, write speed of 4.4GB/s and a low latency of 30 microseconds. It has 1.19M Read 512 byte IOPS and 1.18M Write 512 byte IOPS.
Quality and performance
SSD technology is developing rapidly. Most of the performance measurements used on disk drives with rotating media are also used on SSDs. Performance of flash-based SSDs is difficult to benchmark because of the wide range of possible conditions. In a test performed in 2010 by Xssist, using
IOmeterIometer is an I/O subsystem measurement and characterization tool for single and clustered systems. It is used as a benchmark and troubleshooting tool and is easily configured to replicate the behaviour of many popular applications...
, 4 KB random 70% read/30% write, queue depth 4, the IOPS delivered by the Intel X25-E 64 GB G1 started around 10,000 IOPs, and dropped sharply after 8 minutes to 4,000 IOPS, and continued to decrease gradually for the next 42 minutes. IOPS vary between 3,000 to 4,000 from around 50 minutes onwards for the rest of the 8+ hours test run.
Write amplification is the major reason for the change in performance of an SSD over time. Enterprise grade drives try to avoid this performance variation by increasing over provisioning, and by employing wear-leveling algorithms that move data around only when the drives are not being heavily utilized.
Applications
Until 2009, SSDs were mainly used in those aspects of
mission criticalMission critical refers to any factor of a system whose failure will result in the failure of business operations. That is, it is critical to the organization's 'mission'....
applications where the speed of the storage system needed to be as fast as possible. Since flash memory has become a common component of SSDs, the falling prices and increased densities have made it more financially attractive for many other applications. Organizations that can benefit from faster access of system data include equity trading companies,
telecommunicationTelecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
corporations,
streaming mediaStreaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...
and
video editingThe term video editing can refer to:* Linear video editing, using video tape* Non-linear editing system , using computers with video editing software* Offline editing* Online editing...
firms. The list of applications which could benefit from faster storage is vast. Any company can assess the
ROIIn finance, rate of return , also known as return on investment , rate of profit or sometimes just return, is the ratio of money gained or lost on an investment relative to the amount of money invested. The amount of money gained or lost may be referred to as interest, profit/loss, gain/loss, or...
from adding SSDs to their own applications to best understand if that will be cost effective for them.
Flash-based solid-state drives can be used to create network appliances from general-purpose
personal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
hardware. A
write protectedWrite protection is any physical mechanism that prevents modification or erasure of valuable data on a device. Most commercial software, audio and video is sold pre-protected.-Examples:...
flash drive containing the operating system and application software can substitute for larger, less reliable disk drives or CD-ROMs. Appliances built this way can provide an inexpensive alternative to expensive router and firewall hardware.
SSDs based on an SD card with a live SD operating system are easily write-locked. Combined with a
cloud computingCloud computing is the delivery of computing as a service rather than a product, whereby shared resources, software, and information are provided to computers and other devices as a utility over a network ....
environment or other writable medium, to maintain
persistencePersistence in computer science refers to the characteristic of state that outlives the process that created it. Without this capability, state would only exist in RAM, and would be lost when this RAM loses power, such as a computer shutdown....
, an
OSAn operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
bootedIn computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...
from a write-locked SD card is robust, rugged, reliable, and impervious to permanent corruption. If the running OS degrades, simply turning the machine off and then on returns it back to its initial virgin uncorrupted state and thus is particularly solid. The SD card installed OS does not require removal of corrupted components since it was write-locked though any written media may need to be restored.
In 2011 Intel introduced a caching mechanism for their Z68 chipset (and mobile derivatives) called
Smart Response TechnologyIn computing, Smart Response Technology is a proprietary caching mechanism introduced in 2011 by Intel for their Z68 chipset , which allows a SATA solid-state drive to function as cache for a hard disk drive.SRT is implemented in the device driver and firmware...
, which allows a
SATASata is a traditional dish from the Malaysian state of Terengganu, consisting of spiced fish meat wrapped in banana leaves and cooked on a grill.It is a type of Malaysian fish cake, or otak-otak...
SSD to be used as a
cacheIn computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...
(configurable as write-through or write-back) for a conventional, magnetic hard disk drive. A similar technology is available on
HighPointHighpoint can refer to:*Highpoint, Florida, an unincorporated community near Tampa Bay*Highpoint Center for Printmaking, a print workshop in Minneapolis*Highpoint Shopping Centre in Melbourne, Australia*Highpoint I, a set of apartment buildings in London...
's RocketHybrid PCIe card.
Hybrid driveA Hybrid Drive, Hybrid Hard Drive , or Hybrid Hard Disk Drive is a type of large-buffer computer hard disk drive. It is different from standard hard drives in that it integrates a cache using non-volatile memory or even a small solid-state drive...
s (H-HDSs) are based on the same principle, but integrate some amount of flash memory on board of a conventional drive instead of using a separate SSD. The flash layer in these drives can be accessed independently from the
magnetic storageMagnetic storage and magnetic recording are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using...
by the host using ATA-8 commands, allowing the operating system to manage it. For example Microsoft's ReadyDrive technology explicitly stores portions of the hibernation file in the cache of these drives when the system hibernates, making the subsequent resume faster.
SSD-optimized file systems
There are a number of computer
file systemA file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
s which are optimized for solid-state drives. Some of the more popular or notable are listed below.
Microsoft Windows
Versions of
WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
prior to Windows 7 are optimized for hard disk drives rather than SSDs.
Windows VistaWindows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
includes
ReadyBoostReadyBoost is a disk cache component of Microsoft Windows, first introduced with Microsoft's Windows Vista in 2006 and bundled with Windows 7 in 2009...
to exploit characteristics of USB-connected flash devices, but for SSDs it only improves the default partition alignment to prevent read-modify-write operations which reduce the speed of the SSD. This is because most SSDs are typically aligned on 4 KB sectors and most OSes are based on 512 byte sectors with the default partition set up unaligned . The proper alignment really does not help the SSD's endurance over the life of the drive, however some Vista operations, if not disabled, can shorten the life of the SSD. Disk
defragmentationIn the maintenance of file systems, defragmentation is a process that reduces the amount of fragmentation. It does this by physically organizing the contents of the mass storage device used to store files into the smallest number of contiguous regions . It also attempts to create larger regions of...
should be disabled because the location of the file components on an SSD doesn't significantly impact its performance, but moving the files to make them contiguous using the Windows Defrag routine will cause unnecessary write wear on the limited number of P/E cycles on the SSD. The Superfetch feature will not materially improve the performance of the system and causes additional overhead in the system and SSD, although it does not cause wear.
Windows 7 is optimized for SSDs as well as for traditional magnetic hard disks. The OS looks for the presence of an SSD and operates differently with that drive. If an SSD is present, Windows 7 will disable disk defragmentation, Superfetch, ReadyBoost, and other boot-time and application prefetching operations. It also includes support for the
TRIMIn computing, a TRIM command allows an operating system to inform a solid-state drive which blocks of data are no longer considered in use and can be wiped internally. While TRIM is frequently spelled in capital letters, it is not an acronym; it is merely a command name.TRIM was introduced soon...
command to reduce garbage collection of data which the OS has already determined is no longer valid. Without support for TRIM, the SSD would be unaware of this data being invalid and would unnecessarily continue to rewrite this data during garbage collection causing further wear on the SSD.
ZFS
Solaris as of version 10 Update 6 (released in October 2008), and recent versions of
OpenSolarisOpenSolaris was an open source computer operating system based on Solaris created by Sun Microsystems. It was also the name of the project initiated by Sun to build a developer and user community around the software...
and Solaris Express Community Edition can use SSDs as a performance booster for
ZFSIn computing, ZFS is a combined file system and logical volume manager designed by Sun Microsystems. The features of ZFS include data integrity verification against data corruption modes , support for high storage capacities, integration of the concepts of filesystem and volume management,...
. A low-latency SSD can be used for the ZFS Intent Log (ZIL), where it is named the SLOG. This is used every time a synchronous write to the disk occurs. An SSD (not necessarily with a low-latency) may also be used for the level 2
Adaptive Replacement CacheAdaptive Replacement Cache is a page replacement algorithm withbetter performance than LRU developed at the IBM Almaden Research Center. This is accomplished by keeping track of both Frequently Used and Recently Used pages plus a recent eviction history for both...
(L2ARC), which is used to cache data for reading. When used either alone or in combination, large increases in performance are generally seen.
FreeBSD
In addition to ZFS features described above,
UFSThe Unix file system is a file system used by many Unix and Unix-like operating systems. It is also called the Berkeley Fast File System, the BSD Fast File System or FFS...
supports the
TRIMIn computing, a TRIM command allows an operating system to inform a solid-state drive which blocks of data are no longer considered in use and can be wiped internally. While TRIM is frequently spelled in capital letters, it is not an acronym; it is merely a command name.TRIM was introduced soon...
command.
Linux systems
The Linux kernel supports the TRIM function starting with version 2.6.33. The
ext4The ext4 or fourth extended filesystem is a journaling file system for Linux, developed as the successor to ext3.It was born as a series of backward compatible extensions to ext3, many of them originally developed by Cluster File Systems for the Lustre file system between 2003 and 2006, meant to...
file system is supported when mounted using the "discard" parameter. The most recent disk utilities (and therefore installation software that make use of them) also apply proper partition alignment.
Mac OS X
Mac OS X 10.7 (Lion) supports TRIM, as does OS X 10.6.8 Snow Leopard. It is possible to add TRIM to versions earlier than 10.6.8.
Standardization organizations
The following are noted standardization organizations and bodies that work to create standards for solid-state drives (and other computer storage devices). It also includes organizations who promote the use of solid-state drives. This is not necessarily an exhaustive list.
| Organization or Committee |
Subcommittee of: |
Purpose |
| INCITS |
N/A |
Coordinates technical standards activity between ANSI in the USA and joint ISO/IEC committees worldwide |
| T10 |
INCITS |
SCSI Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
|
| T11 |
INCITS |
FCFibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
|
| T13 |
INCITS |
ATAParallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...
|
| JEDEC The JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...
|
N/A |
Develops open standards and publications for the microelectronics industry |
| JC-64.8 The JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...
|
JEDEC |
Focuses on solid-state drive standards and publications |
| NVMHCI |
N/A |
Provides standard software and hardware programming interfaces for nonvolatile memory subsystems |
| SATA-IO Serial ATA International Organization is an independent, non-profit organization which provides the computing industry with guidance and support for implementing the SATA specification. SATA-IO was developed by and for leading industry companies...
|
N/A |
Provides the industry with guidance and support for implementing the SATA specification |
| SFF Committee The Small Form Factor committee is an ad hoc electronics industry group formed to quickly develop interoperability specifications ....
|
N/A |
Works on storage industry standards needing prompt attention when not addressed by other standards committees |
| SNIA An association of producers and consumers of storage networking products, whose goal is to further storage networking technology and applications.The Storage Networking Industry Association, or SNIA, was incorporated in December, 1997, and is a registered 501 non-profit trade association...
|
N/A |
Develops and promotes standards, technologies, and educational services in the management of information |
| SSSI |
SNIA |
Fosters the growth and success of solid state storage |
A
solid-state drive (SSD), sometimes called a
solid-state disk or
electronic disk, is a
data storage devicethumb|200px|right|A reel-to-reel tape recorder .The magnetic tape is a data storage medium. The recorder is data storage equipment using a portable medium to store the data....
that uses solid-state
memoryComputer data storage, often called storage or memory, refers to computer components and recording media that retain digital data. Data storage is one of the core functions and fundamental components of computers....
to store
persistent dataPersistence in computer science refers to the characteristic of state that outlives the process that created it. Without this capability, state would only exist in RAM, and would be lost when this RAM loses power, such as a computer shutdown....
with the intention of providing access in the same manner of a traditional block i/o hard disk drive. SSDs are distinguished from traditional magnetic disks such as hard disk drives (HDDs) or
floppy diskA floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
, which are electromechanical devices containing spinning
disksDisk storage or disc storage is a general category of storage mechanisms, in which data are digitally recorded by various electronic, magnetic, optical, or mechanical methods on a surface layer deposited of one or more planar, round and rotating disks...
and movable
read/write headsDisk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...
. In contrast, SSDs use
microchipAn integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s that retain data in non-volatile memory chips and contain no
moving partsThe moving parts of a machine are those parts of it that move. Machines comprise both moving and fixed parts. The moving parts have controlled and constrained motions....
. Compared to electromechanical HDDs, SSDs are typically less susceptible to physical shock, are silent, have lower
access timeAccess time is the time delay or latency between a request to an electronic system, and the access being completed or the requested data returned....
and
latencyLatency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...
, but are more expensive per
gigabyteThe gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...
(GB). SSDs use the same interface as hard disk drives, thus easily replacing them in most applications.
, most SSDs use NAND-based flash memory, which retains memory even without power. SSDs using volatile
random-access memoryRandom access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...
(RAM) also exist for situations that require even faster access, but do not necessarily need data
persistencePersistence in computer science refers to the characteristic of state that outlives the process that created it. Without this capability, state would only exist in RAM, and would be lost when this RAM loses power, such as a computer shutdown....
after power loss, or use external power or batteries to maintain the data after power is removed.
A
hybrid driveA Hybrid Drive, Hybrid Hard Drive , or Hybrid Hard Disk Drive is a type of large-buffer computer hard disk drive. It is different from standard hard drives in that it integrates a cache using non-volatile memory or even a small solid-state drive...
combines the features of an HDD and an SSD into one unit, containing a large HDD and a smaller SSD cache to improve performance of frequently accessed files. These can offer near-SSD performance in most applications (such as system startup and loading applications) at a lower price than an SSD. These are not suitable for data-intensive work, nor do they offer the other advantages of SSDs.
Development and history
Early SSDs using RAM and similar technology
The origins of SSDs came from the 1950s using two similar technologies,
magnetic core memoryMagnetic-core memory was the predominant form of random-access computer memory for 20 years . It uses tiny magnetic toroids , the cores, through which wires are threaded to write and read information. Each core represents one bit of information...
and card capacitor read-only store (CCROS). These auxiliary memory units, as they were called at the time, emerged during the era of
vacuum tubeIn electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
computers. But with the introduction of cheaper
drum storage unitsDrum memory is a magnetic data storage device and was an early form of computer memory widely used in the 1950s and into the 1960s, invented by Gustav Tauschek in 1932 in Austria....
, their use was discontinued.
Later, in the 1970s and 1980s, SSDs were implemented in semiconductor memory for early supercomputers of
IBMInternational Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
,
AmdahlAmdahl Corporation is an information technology company which specializes in IBM mainframe-compatible computer products. Founded in 1970 by Dr. Gene Amdahl, a former IBM employee, it has been a wholly owned subsidiary of Fujitsu since 1997...
and
CrayCray Inc. is an American supercomputer manufacturer based in Seattle, Washington. The company's predecessor, Cray Research, Inc. , was founded in 1972 by computer designer Seymour Cray. Seymour Cray went on to form the spin-off Cray Computer Corporation , in 1989, which went bankrupt in 1995,...
; however, the prohibitively high price of the built-to-order SSDs made them quite seldom used. In the late 1970s, General Instruments produced an electrically alterable ROM (EAROM) which operated somewhat like the later NAND flash memory, but the inability to achieve a 10-year life was not practical and many companies abandoned the technology. In 1976
DataramDataram Corporation is an international manufacturer of computer memory, storage, and software products, founded in 1967 as a supplier of original equipment memory to Digital Equipment Corporation.-Company overview:...
started selling a product called
BULK CORE providing up to 2MB of solid state storage compatible with
DECDigital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
and
Data GeneralData General was one of the first minicomputer firms from the late 1960s. Three of the four founders were former employees of Digital Equipment Corporation. Their first product, the Data General Nova, was a 16-bit minicomputer...
computers.
Texas Memory SystemsTexas Memory Systems, Inc. is a privately held American corporation that designs and manufacturers solid-state disks and digital signal processors . TMS was founded in 1978 and that same year introduced their first solid-state drive, followed by their first digital signal processor...
introduced a 16
kilobyteThe kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
(KB) RAM solid-state drive in 1978 to be used by oil companies for
seismic dataReflection seismology is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismic source of energy, such as dynamite/Tovex, a specialized air gun or a...
acquisition. The following year, StorageTek developed the first modern type of solid-state drive.
The
Sharp PC-5000The Sharp PC-5000 was a pioneering laptop computer, announced by Sharp Corporation of Japan in 1983. Like the GRiD Compass, which preceded it, and its contemporary the Gavilan SC, it employed a clamshell design in which the display closes over the keyboard....
, introduced in 1983, used 128 kilobyte solid-state storage cartridges, containing
bubble memoryBubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles or domains, each storing one bit of data...
. In 1984 Tallgrass Technologies Corporation had a tape back up unit of 40 MB with a solid state 20 MB unit built in. The 20 MB unit could be used instead of a hard drive. In September 1986, Santa Clara Systems introduced BatRam, 4
megabyteThe megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
(MB) mass storage system expandable to 20 MB using 4 MB memory modules. The package included a rechargeable battery to preserve the memory chip contents when the array was not powered. 1987 saw the entry of
EMC CorporationEMC Corporation , a Financial Times Global 500, Fortune 500 and S&P 500 company, develops, delivers and supports information infrastructure and virtual infrastructure hardware, software, and services. EMC is headquartered in Hopkinton, Massachusetts, USA.Former Intel executive Richard Egan and his...
into the SSD market, with drives introduced for the mini-computer market. However, by 1993 EMC had exited the SSD market.
Software-based
RAM DiskA RAM disk or RAM drive is a block of RAM that a computer's software is treating as if the memory were a disk drive...
s are still used today because they are an
order of magnitudeAn order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. In its most common usage, the amount being scaled is 10 and the scale is the exponent being applied to this amount...
faster than the fastest SSD, but they consume CPU resources and cost much more on a per GB basis.
Flash-based SSDs
In 1994,
STEC, Inc.STEC, Inc. is a multinational company and a leader in enterprise solid-state drive .The company is headquartered in Santa Ana, California...
bought Cirrus Logic’s flash controller operation, allowing the company to enter the flash memory business for consumer electronic devices.
In 1995,
M-SystemsM-Systems Ltd., was a Nasdaq-listed Israeli producer of Flash memory storage products founded in 1989 by Dov Moran and based in Kfar Sava, Israel. They were best known for developing and patenting the first flash drive, marketed in 1995 as DiskOnChip, and the first USB flash drive, marketed in...
introduced flash-based solid-state drives. They had the advantage of not requiring batteries to maintain the data in the memory (required by the prior volatile memory systems), but were not as fast as the DRAM-based solutions. Since then, SSDs have been used successfully as HDD replacements by the military and aerospace industries, as well as for other mission-critical applications. These applications require the exceptional mean time between failures (MTBF) rates that solid-state drives achieve, by virtue of their ability to withstand extreme shock, vibration and temperature ranges.
BiTMICRO made a number of introductions and announcements in 1999 around flash-based SSDs including an 18 GB 3.5 in SSD. Fusion-io announced a PCIe-based SSD with 100,000
input/output operations per secondIOPS is a common performance measurement used to benchmark computer storage devices like hard disk drives , solid state drives , and storage area networks...
(IOPS) of performance in a single card with capacities up to 320 gigabytes in 2007. At Cebit 2009, OCZ demonstrated a 1
terabyteThe terabyte is a multiple of the unit byte for digital information. The prefix tera means 1012 in the International System of Units , and therefore 1 terabyte is , or 1 trillion bytes, or 1000 gigabytes. 1 terabyte in binary prefixes is 0.9095 tebibytes, or 931.32 gibibytes...
(TB) flash SSD using a PCI Express ×8 interface. It achieves a maximum write speed of 654 megabytes per second (MB/s) and maximum read speed of 712 MB/s. In December 2009,
Micron TechnologyMicron Technology, Inc. is an American multinational corporation based in Boise, Idaho, USA, best known for producing many forms of semiconductor devices. This includes DRAM, SDRAM, flash memory, SSD and CMOS image sensing chips. Consumers may be more familiar with its consumer brand Crucial...
announced the world's first SSD using a 6 gigabits per second (Gbit/s) or 600 (MB/s)
SATASata is a traditional dish from the Malaysian state of Terengganu, consisting of spiced fish meat wrapped in banana leaves and cooked on a grill.It is a type of Malaysian fish cake, or otak-otak...
interface.
Enterprise flash drives
Enterprise flash drives (EFDs) are designed for applications requiring high I/O performance (
IOPSIOPS is a common performance measurement used to benchmark computer storage devices like hard disk drives , solid state drives , and storage area networks...
), reliability, and energy efficiency. In most cases an EFD is an SSD with a higher set of specifications compared to SSDs that would typically be used in notebook computers. The term was first used by EMC in January 2008, to help them identify SSD manufacturers who would provide products meeting these higher standards. There are no standards bodies who control the definition of EFDs, so any SSD manufacturer may claim to produce EFDs when they may not actually meet the requirements. Likewise there may be other SSD manufacturers that meet the EFD requirements without being called EFDs.
Architecture and function
The key components of an SSD are the controller and the memory to store the data. The primary memory component in an SSD had been
DRAMDram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...
volatile memoryVolatile memory, also known as volatile storage, is computer memory that requires power to maintain the stored information, unlike non-volatile memory which does not require a maintained power supply...
since they were first developed, but since 2009 it is more commonly NAND flash
non-volatile memoryNon-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...
. Other components play a less significant role in the operation of the SSD and vary between manufacturers.
Controller
Every SSD includes a
controllerA flash memory controller manages the data stored on flash memory and communicates with a computer or electronic device. Flash memory controllers can be designed for operating in low duty-cycle environments like SD cards, CompactFlash cards, or other similar media for use in digital cameras, PDAs,...
that incorporates the electronics that bridge the NAND memory components to the host
computerA computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
. The controller is an embedded processor that executes firmware-level code and is one of the most important factors of SSD performance. Some of the functions performed by the controller include:
- Error correction (ECC)
- Wear leveling
Wear leveling is a technique for prolonging the service life of some kinds of erasable computer storage media, such as Flash memory used in solid-state drives and USB Flash drives...
- Bad block
Bad Sector is an ambient/noise project formed in 1992 in Tuscany, Italy by Massimo Magrini. While working at the Computer Art Lab of ISTI in Pisa , he developed original gesture interfaces that he uses in live performances: 'Aerial Painting Hand' , 'UV-Stick' Bad Sector is an ambient/noise...
mapping
- Read scrubbing
Memory scrubbing is the process of detecting and correcting bit errors in computer memory by using error-detecting codes like ECC.-Motivation for scrubbing:...
and read disturb management
- Read and write caching
In computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...
- Garbage collection
- Encryption
In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...
The performance of the SSD can scale with the number of parallel NAND flash chips used in the device. A single NAND chip is relatively slow, due to narrow (8/16 bit) asynchronous IO interface, and additional high latency of basic IO operations (typical for SLC NAND, ~25
μsA microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
to fetch a 4K page from the array to the IO buffer on a read, ~250 μs to commit a 4K page from the IO buffer to the array on a write, ~2 ms to erase a 256 kiB block). When multiple NAND devices operate in parallel inside an SSD, the bandwidth scales, and the high latencies can be hidden, as long as enough outstanding operations are pending and the load is evenly distributed between devices. Micron and Intel initially made faster SSDs by implementing
data stripingIn computer data storage, data striping is the technique of segmenting logically sequential data, such as a file, in a way that accesses of sequential segments are made to different physical storage devices. Striping is useful when a processing device requests access to data more quickly than a...
(similar to
RAIDRAID is a storage technology that combines multiple disk drive components into a logical unit...
0) and interleaving in their architecture. This enabled the creation of ultra-fast SSDs with 250 MB/s effective read/write speeds with the SATA 3 Gb/s interface in 2009. Two years later and continuing to leverage this parallel flash connectivity, SandForce released consumer-grade SATA 6 Gb/s SSD controllers which support 500 MB/s read/write speeds.
Flash memory-based
Most SSD manufacturers use
non-volatile NAND flash memoryFlash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
in the construction of their SSDs because of the lower cost compared to
DRAMDram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...
. and the ability to retain the data without a constant power supply, ensuring data persistence through sudden power outages. Flash memory SSDs are slower than DRAM solutions, and some early designs were even slower than HDDs after continued use. This problem was resolved by controllers that came out in 2009 and later.
Flash memory-based solutions are typically packaged in standard disk drive form factors (1.8-, 2.5-, and 3.5-inch), or smaller unique and compact layouts because of the compact memory.
Lower priced drives usually use
multi-level cellIn electronics, a multi-level cell is a memory element capable of storing more than a single bit of information.MLC NAND flash is a flash memory technology using multiple levels per cell to allow more bits to be stored using the same number of transistors...
(MLC) flash memory, which is slower and less reliable than single-level cell (SLC) flash memory. This can be mitigated or even reversed by the internal design structure of the SSD, such as interleaving, changes to writing algorithms, and higher over-provisioning (more excess capacity) with which the wear-leveling algorithms can work.
DRAM-based
SSDs based on volatile memory such as DRAM are characterized by ultrafast data access, generally less than 10
microsecondA microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
s, and are used primarily to accelerate applications that would otherwise be held back by the latency of flash SSDs or traditional HDDs. DRAM-based SSDs usually incorporate either an internal battery or an external AC/DC adapter and
backupIn information technology, a backup or the process of backing up is making copies of data which may be used to restore the original after a data loss event. The verb form is back up in two words, whereas the noun is backup....
storage systems to ensure data persistence while no power is being supplied to the drive from external sources. If power is lost, the battery provides power while all information is copied from random access memory (RAM) to back-up storage. When the power is restored, the information is copied back to the RAM from the back-up storage, and the SSD resumes normal operation (similar to the
hibernateHibernation in computing is powering down a computer while retaining its state.Upon hibernation, the computer saves the contents of its random access memory to a hard disk or other non-volatile storage...
function used in modern operating systems).
SSDs of this type are usually fitted with DRAM modules of the same type used in regular PCs and servers, which can be swapped out and replaced by larger modules.
A
remote, indirect memory-access disk (RIndMA Disk) uses a secondary computer with a fast network or (direct)
InfinibandInfiniBand is a switched fabric communications link used in high-performance computing and enterprise data centers. Its features include high throughput, low latency, quality of service and failover, and it is designed to be scalable...
connection to act like a RAM-based SSD, but the new faster flash memory based SSDs already available in 2009 are making this option not as cost effective.
Cache or buffer
A flash-based SSD typically uses a small amount of DRAM as a cache, similar to the cache in Hard disk drives. A directory of block placement and wear leveling data is also kept in the cache while the drive is operating. Data is not permanently stored in the cache. One SSD controller manufacturer,
SandForceSandForce is an American "fabless" semiconductor company based in Milpitas, California, that designs and manufactures flash memory controllers for solid-state drives . On October 26th 2011 it was acquired by LSI Corporation....
, does not use an external DRAM cache on their designs, but still achieve very high performance. Eliminating the external DRAM enables a smaller footprint for the other flash memory components in order to build even smaller SSDs.
Battery or super capacitor
Another component in higher performing SSDs is a capacitor or some form of battery. These are necessary to maintain data integrity such that the data in the cache can be flushed to the drive when power is dropped; some may even hold power long enough to maintain data in the cache until power is resumed. In the case of MLC flash memory, a problem called
lower page corruption can occur when MLC flash memory loses power while programming an upper page. The result is data written previously and presumed safe can be corrupted if the memory is not supported by a super capacitor in the event of a sudden power loss. This problem does not exist with SLC flash memory.
Host interface
The host interface is not specifically a component of the SSD, but it is a key part of the drive. The interface is usually incorporated into the controller discussed above. The interface is generally one of the interfaces found in HDDs. They include:
- Serial ATA
Serial ATA is a computer bus interface for connecting host bus adapters to mass storage devices such as hard disk drives and optical drives...
- Serial attached SCSI
Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,...
(generally found on serversIn the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
)
- PCI Express
PCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...
- Fibre Channel
Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
(almost exclusively found on servers)
- USB
- Parallel ATA
Parallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...
(IDEParallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...
) interface (mostly replaced by SATA)
- (Parallel) SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
(generally found on servers; mostly replaced by SAS; last SCSI-based SSD introduced in 2004)
Form factor
The size and shape of any device is largely driven by the size and shape of the components used to make that device. Traditional HDDs and optical drives are designed around the rotating platter or
optical discIn computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...
along with the spindle motor inside. If an SSD is made up of various interconnected integrated circuits (ICs) and an interface connector, then its shape could be virtually anything imaginable because it is no longer limited to the shape of rotating media drives. Some solid state storage solutions come in a larger chassis that may even be a rack-mount form factor with numerous SSDs inside. They would all connect to a common bus inside the chassis and connect outside the box with a single connector.
Standard HDD form factors
The benefit of using a current HDD form factor would be to take advantage of the extensive infrastructure already in place to mount and connect the drives to the host system. These traditional form factors are known by the size of the rotating media, e.g., 5.25", 3.5", 2.5", 1.8", not by the dimensions of the drive casing.
Box form factors
Many of the DRAM-based solutions use a box that is often designed to fit in a rack-mount system. The number of DRAM components required to get sufficient capacity to store the data along with the backup power supplies requires a larger space than traditional HDD form factors.
Bare-board form factors
Form factors which were more common to memory modules are now being used by SSDs to take advantage of their flexibility in laying out the components. Some of these include
PCIePCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...
, mini PCIe, mini-DIMM, MO-297, and many more. The SATADIMM from Viking Modular uses an empty DDR3 DIMM slot on the motherboard to provide power to the drive with a separate SATA connector to provide the data connection back to the computer. The result is an easy to install SSD with a capacity equal to drives that typically take a full 2.5 in expansion slot. At least one manufacturer, InnoDisk, is producing a drive that sits directly on the SATA connector on the motherboard without any other support or mechanical mount. Some SSDs are based on the PCIe form factor and connect both the data interface and power through the PCIe connector to the host. These drives can use either direct PCIe flash controllers or a PCIe-to-SATA bridge device which then connects to SATA flash controller(s).
Ball grid array form factors
In the early 2000s, a few companies introduced SSDs in
Ball Grid ArrayA ball grid array is a type of surface-mount packaging used for integrated circuits.- Description :The BGA is descended from the pin grid array , which is a package with one face covered with pins in a grid pattern. These pins conduct electrical signals from the integrated circuit to the printed...
(BGA) form factors, such as M-Systems’ (now
SanDiskSanDisk Corporation is an American multinational corporation that designs, develops and manufactures data storage solutions in a range of form factors using the flash memory, controller and firmware technologies. It was founded in 1988 by Dr. Eli Harari and Sanjay Mehrotra, non-volatile memory...
) DiskOnChip and
Silicon Storage TechnologySilicon Storage Technology, Inc. is a Sunnyvale, California, USA, technology company producing non-volatile memory devices and related products.It was founded by Bing Yeh in 1989....
’s NANDrive (now produced by
Greenliant SystemsGreenliant Systems is a manufacturer of flash memory, solid-state storage and controller semiconductors for embedded system, data center and mobile products. Greenliant was founded in 2010, when former Silicon Storage Technology CEO Bing Yeh acquired several flash memory assets from the company...
), and
MemorightMemoright is a Taiwan based storage products house founded in March 2006.It produced a 2.5inch SSD with a claimed read/write speed of 100mb/s, the fastest SSD available at the time....
's M1000 for use in embedded systems. The main benefits of BGA SSDs are their low power consumption, small chip package size to fit into compact subsystems, and that they can be soldered directly onto a system motherboard to reduce adverse effects from vibration and shock.
Comparison of SSD with hard disk drives
Making a comparison between SSDs and ordinary (spinning) HDDs is difficult. Traditional HDD
benchmarksIn computing, a benchmark is the act of running a computer program, a set of programs, or other operations, in order to assess the relative performance of an object, normally by running a number of standard tests and trials against it...
are focused on finding the performance aspects where they are weak, such as rotational latency time and seek time. As SSDs do not spin, or seek, they may show huge superiority in such tests. However, SSDs have challenges with mixed reads and writes, and their performance may degrade over time. SSD testing must start from the (in use) full disk, as the new and empty (fresh out of the box) disk may have much better write performance than it would show after only weeks of use.
Comparisons reflect typical characteristics, and may not hold for a specific device.
| Attribute or characteristic |
Solid-state drive |
Hard disk drive |
| Spin-up Spin-up refers to the process of a traditional hard disk drive accelerating its platters from a stopped state to an operational speed. The period of time taken by the drive to perform this process is referred to as its spin-up time, the average of which is a S.M.A.R.T. attribute. The required...
time |
Almost Instantaneous; nothing mechanical to "spin up". May need a few milliseconds to come out of an automatic power-saving mode. |
May take several seconds. With a large number of drives, spin-up may need to be staggered to limit total power drawn. |
| Random access In computer science, random access is the ability to access an element at an arbitrary position in a sequence in equal time, independent of sequence size. The position is arbitrary in the sense that it is unpredictable, thus the use of the term "random" in "random access"...
time |
About 0.1 ms - many times faster than HDDs because data is accessed directly from the flash memory |
Ranges from 5–10 ms due to the need to move the heads and wait for the data to rotate under the read/write head Disk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...
|
| Read latency time |
Generally low because the data can be read directly from any location; In applications where hard disk seeks are the limiting factor, this results in faster boot and application launch times (see Amdahl's law Amdahl's law, also known as Amdahl's argument, is named after computer architect Gene Amdahl, and is used to find the maximum expected improvement to an overall system when only part of the system is improved...
). |
Generally high since the mechanical components require additional time to get aligned |
| Consistent read performance |
Read performance does not change based on where data is stored on an SSD |
If data is written in a fragmented way, reading back the data will have varying response times |
DefragmentationIn the maintenance of file systems, defragmentation is a process that reduces the amount of fragmentation. It does this by physically organizing the contents of the mass storage device used to store files into the smallest number of contiguous regions . It also attempts to create larger regions of...
|
SSDs do not benefit from defragmentation because there is little benefit to reading data sequentially (beyond typical FS block sizes) and any defragmentation process adds additional writes on the NAND flash that already have a limited cycle life. |
HDDs may require defragmentation after continued operations or erasing and writing data, especially involving large files . |
AcousticAcoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...
levels |
SSDs have no moving parts and make no sound |
HDDs have moving parts (heads, spindle motor) and have varying levels of sound depending upon model |
Mechanical reliabilityReliability engineering is an engineering field, that deals with the study, evaluation, and life-cycle management of reliability: the ability of a system or component to perform its required functions under stated conditions for a specified period of time. It is often measured as a probability of...
|
A lack of moving parts virtually eliminates mechanical breakdowns |
HDDs have many moving parts that are all subject to failure over time |
| Susceptibility to environmental factors |
No flying heads or rotating platters to fail as a result of shock, altitude, or vibration |
The flying heads and rotating platters are generally susceptible to shock, altitude, and vibration |
| Magnetic Magnetic storage and magnetic recording are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using...
susceptibility |
No impact on flash memory |
Magnets or magnetic surges can alter data on the media |
| Weight and size |
The weight of flash memory and the circuit board material are very light compared to HDDs |
Higher performing HDDs require heavier components than laptop HDDs (which are light, but not as light as SSDs) |
| Parallel operation |
Some flash controllers can have multiple flash chips reading and writing different data simultaneously |
HDDs have multiple heads (one per platter) but they are connected, and share one positioning motor. |
| Write longevity |
Flash-based SSDs have a limited number of writes (1-5 million or more) over the life of the drive. Software controllers manage this limitation in such a way that drives can last for many decades before failure. SSDs based on DRAM do not have a limited number of writes. |
Magnetic media do not have a similar limited number of writes but are susceptible to eventual mechanical failure. |
| Software encryption limitations |
NAND flash memory cannot be overwritten, but has to be rewritten to previously erased blocks. If a software encryption In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...
program encrypts data already on the SSD, the overwritten data is still unsecured, unencrypted, and accessible (drive-based hardware encryption does not have this problem). Also data cannot be securely erased by overwriting the original file without special "Secure Erase" procedures built into the drive. |
HDDs can overwrite data directly on the drive in any particular sector. |
| Cost per capacity |
, NAND flash SSDs cost about (US)$.90–2.00 per GB |
, HDDs cost about (US)$0.05/GB for 3.5 in and $0.10/GB for 2.5 in drives |
| Storage capacity |
, SSDs come in different sizes up to 2TB but are typically not larger than 64-256GB, due to their high cost per GB. |
, HDDs are typically 500GB-1TB but drives as large as 2 or 3 TB are also available. |
| Read/write performance symmetry |
Less expensive SSDs typically have write speeds significantly lower than their read speeds. Higher performing SSDs have a balanced read and write speed. |
HDDs generally have slightly lower write speeds than their read speeds. |
| Free block availability and TRIM Trim may refer to:* Cutting small pieces off something** Book trimming, a stage of the publishing process** Editing*** Editing a posting style in online discourse** Pruning, trimming as a form of pruning often used on trees-Places:...
|
SSD write performance is significantly impacted by the availability of free, programmable blocks. Previously written data blocks that are no longer in use can be reclaimed by TRIM; however, even with TRIM, fewer free, programmable blocks translates into reduced performance. |
HDDs are not affected by free blocks or the operation (or lack) of the TRIM command |
| Power consumption |
High performance flash-based SSDs generally require 1/2 to 1/3 the power of HDDs; High performance DRAM SSDs generally require as much power as HDDs and consume power when the rest of the system is shut down. |
High performance HDDs generally require between 12-18 watts; drives designed for notebook computers are typically 2 watts. |
Comparison of SSD with memory cards
While it is true that both memory cards and most SSDs use flash memory, they serve very different markets and purposes. Each has a number of different attributes which are optimized and adjusted to best meet the needs of particular users. Some of these characteristics include power consumption, performance, size, and reliability.
SSDs were originally designed for use in a computer system. The first units were intended to replace or augment hard disk drives, so the operating system recognized them as a hard drive. Originally, solid state drives were even shaped and mounted in the computer like hard drives. Later SSDs became smaller and more compact, eventually developing their own unique form factors. The SSD was designed to be installed one time inside the computer and only have it removed when servicing or upgrading it.
In contrast, memory cards like
CompactFlashCompactFlash is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994...
(CF),
Secure DigitalSecure Digital is a non-volatile memory card format developed by the SD Card Association for use in portable devices. The SD technology is used by more than 400 brands across dozens of product categories and more than 8,000 models, and is considered the de-facto industry standard.Secure Digital...
(SD), Memory Stick, and xD-Picture Card were all originally designed for digital cameras and later found their way into cell phones, gaming devices, and GPS units. Nearly all memory cards are smaller in size than SSDs and they were engineered to be inserted and removed repeatedly. There are adapters which enable some memory cards like the CF card to interface to a computer as an SSD, but they are not intended to be the primary storage device in the computer. The typical CF card interface is generally 3-4 times slower than is available on SSDs.
Commercialization
Cost and capacity
The technological trend of
2 yearMoore's law describes a long-term trend in the history of computing hardware: the number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years....
50% decline in costs is no longer possible in NAND flash as it approaches its terminal node. Instead NAND makers anticipate more modest cost declines in the period 2011-2015. Capacities in client SSDs are typically dictated by cost concerns rather than technical limitations of NAND storage.
Availability
Solid-state drive (SSD) technology has been marketed to the military and niche industrial markets since the mid-1990s..
Along with the emerging enterprise market, SSDs have been appearing in ultra-mobile PCs and a few lightweight laptop systems, adding significantly to the price of the laptop, depending on the capacity, form factor and transfer speeds. , some manufacturers have begun shipping affordable, fast, energy-efficient drives priced at $350 to computer manufacturers. For low-end applications, a USB flash drive may be obtainable for anywhere from $10 to $100 or so, depending on capacity; alternatively, a
CompactFlashCompactFlash is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994...
card may be paired with a CF-to-IDE or CF-to-SATA converter at a similar cost. Either of these requires that write-cycle endurance issues be managed, either by refraining from storing frequently written files on the drive or by using a
flash file systemA flash file system is a file system designed for storing files on flash memory devices. These are becoming more prevalent as the number of mobile devices is increasing, the cost per memory size decreases, and the capacity of flash memories increases....
. Standard CompactFlash cards usually have write speeds of 7 to 15 MB/s while the more expensive upmarket cards claim speeds of up to 60 MB/s.
One of the first mainstream releases of SSD was the
XO LaptopThe XO-1, previously known as the $100 Laptop, Children's Machine, and 2B1, is an inexpensive subnotebook computer intended to be distributed to children in developing countries around the world, to provide them with access to knowledge, and opportunities to "explore, experiment and express...
, built as part of the One Laptop Per Child project. Mass production of these computers, built for children in developing countries, began in December 2007. These machines use 1,024 MiB SLC NAND flash as primary storage which is considered more suitable for the harsher than normal conditions in which they are expected to be used.
DellDell, Inc. is an American multinational information technology corporation based in 1 Dell Way, Round Rock, Texas, United States, that develops, sells and supports computers and related products and services. Bearing the name of its founder, Michael Dell, the company is one of the largest...
began shipping ultra-portable laptops with SanDisk SSDs on April 26, 2007.
AsusASUSTeK Computer Incorporated is a multinational computer technology and consumer electronics product manufacturer headquartered in Taipei, Taiwan. Its product range includes motherboards, desktops, laptops, monitors, tablet PCs, servers and mobile phones...
released the
Eee PCThe Asus Eee PC is a subnotebook/netbook computer line from ASUSTeK Computer Incorporated, and a part of the Asus Eee product family. At the time of its introduction in late 2007, it was noted for its combination of a light weight, Linux operating system, solid-state drive , and relatively low cost...
subnotebookA subnotebook is a class of laptop computers that are smaller and lighter than a typical laptop....
on October 16, 2007, and after a successful commercial start in 2007, it was expected to ship several million PCs in 2008, with 2, 4 or 8 gigabytes of flash memory. On January 31, 2008, Apple Inc. released the
MacBook AirThe MacBook Air family is a line of Apple ultraportable Macintosh notebook computers.The first-generation MacBook Air was a 13.3"-only model, previously promoted as the World's Thinnest Notebook, introduced at the Macworld Conference & Expo on January 15, 2008. It featured a custom Intel Merom CPU...
, a thin laptop with optional 64 GB SSD. The Apple Store cost was $999 more for this option, as compared to that of an 80 GB 4200 RPM hard disk drive. Another option, the Lenovo
ThinkPadThinkPad is line of laptop computers originally sold by IBM but now produced by Lenovo. They are known for their boxy black design, which was modeled after a traditional Japanese lunchbox...
X300 with a 64 gigabyte SSD, was announced by Lenovo in February 2008, and is, , available to consumers in some countries. On August 26, 2008, Lenovo released ThinkPad X301 with 128GB SSD option which adds approximately $200 US.
In 2008, low end netbooks appeared with SSDs. In 2009, SSDs began to appear in laptops.
On January 14, 2008,
EMCEMC Corporation , a Financial Times Global 500, Fortune 500 and S&P 500 company, develops, delivers and supports information infrastructure and virtual infrastructure hardware, software, and services. EMC is headquartered in Hopkinton, Massachusetts, USA.Former Intel executive Richard Egan and his...
became the first enterprise storage vendor to ship flash-based SSDs into its product portfolio.
In late 2008,
SunSun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
released the
Sun Storage 7000 Unified Storage Systems (codenamed Amber Road), which use both solid state drives and conventional hard drives to take advantage of the speed offered by SSDs and the economy and capacity offered by conventional hard disks.
DellDell, Inc. is an American multinational information technology corporation based in 1 Dell Way, Round Rock, Texas, United States, that develops, sells and supports computers and related products and services. Bearing the name of its founder, Michael Dell, the company is one of the largest...
began to offer optional 256 GB solid state drives on select notebook models in January 2009.
In May 2009, Toshiba launched a laptop with a 512 GB SSD.
, Apple's
MacBook AirThe MacBook Air family is a line of Apple ultraportable Macintosh notebook computers.The first-generation MacBook Air was a 13.3"-only model, previously promoted as the World's Thinnest Notebook, introduced at the Macworld Conference & Expo on January 15, 2008. It featured a custom Intel Merom CPU...
line carries solid state drives as standard.
In December 2010,
OCZOCZ Technology is a manufacturer of computer hardware based in San Jose, California, USA. Since entering the memory market in 2002, OCZ has targeted its products primarily at the computer hardware enthusiast market, first producing performance DDR RAM, Video Cards, USB drives, and various Cooling...
RevoDrive X2 PCIe SSD was available in 100GB to 960GB capacities delivering speeds over 740MB/s sequential speeds and random small file writes up to 120,000 IOPS.
In November 2010, Fusion-io released its highest performing SSD drive named ioDrive Octal utilising PCI-Express x16 Gen 2.0 interface with storage space of 5.12TB, read speed of 6.0GB/s, write speed of 4.4GB/s and a low latency of 30 microseconds. It has 1.19M Read 512 byte IOPS and 1.18M Write 512 byte IOPS.
Quality and performance
SSD technology is developing rapidly. Most of the performance measurements used on disk drives with rotating media are also used on SSDs. Performance of flash-based SSDs is difficult to benchmark because of the wide range of possible conditions. In a test performed in 2010 by Xssist, using
IOmeterIometer is an I/O subsystem measurement and characterization tool for single and clustered systems. It is used as a benchmark and troubleshooting tool and is easily configured to replicate the behaviour of many popular applications...
, 4 KB random 70% read/30% write, queue depth 4, the IOPS delivered by the Intel X25-E 64 GB G1 started around 10,000 IOPs, and dropped sharply after 8 minutes to 4,000 IOPS, and continued to decrease gradually for the next 42 minutes. IOPS vary between 3,000 to 4,000 from around 50 minutes onwards for the rest of the 8+ hours test run.
Write amplification is the major reason for the change in performance of an SSD over time. Enterprise grade drives try to avoid this performance variation by increasing over provisioning, and by employing wear-leveling algorithms that move data around only when the drives are not being heavily utilized.
Applications
Until 2009, SSDs were mainly used in those aspects of
mission criticalMission critical refers to any factor of a system whose failure will result in the failure of business operations. That is, it is critical to the organization's 'mission'....
applications where the speed of the storage system needed to be as fast as possible. Since flash memory has become a common component of SSDs, the falling prices and increased densities have made it more financially attractive for many other applications. Organizations that can benefit from faster access of system data include equity trading companies,
telecommunicationTelecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
corporations,
streaming mediaStreaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...
and
video editingThe term video editing can refer to:* Linear video editing, using video tape* Non-linear editing system , using computers with video editing software* Offline editing* Online editing...
firms. The list of applications which could benefit from faster storage is vast. Any company can assess the
ROIIn finance, rate of return , also known as return on investment , rate of profit or sometimes just return, is the ratio of money gained or lost on an investment relative to the amount of money invested. The amount of money gained or lost may be referred to as interest, profit/loss, gain/loss, or...
from adding SSDs to their own applications to best understand if that will be cost effective for them.
Flash-based solid-state drives can be used to create network appliances from general-purpose
personal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
hardware. A
write protectedWrite protection is any physical mechanism that prevents modification or erasure of valuable data on a device. Most commercial software, audio and video is sold pre-protected.-Examples:...
flash drive containing the operating system and application software can substitute for larger, less reliable disk drives or CD-ROMs. Appliances built this way can provide an inexpensive alternative to expensive router and firewall hardware.
SSDs based on an SD card with a live SD operating system are easily write-locked. Combined with a
cloud computingCloud computing is the delivery of computing as a service rather than a product, whereby shared resources, software, and information are provided to computers and other devices as a utility over a network ....
environment or other writable medium, to maintain
persistencePersistence in computer science refers to the characteristic of state that outlives the process that created it. Without this capability, state would only exist in RAM, and would be lost when this RAM loses power, such as a computer shutdown....
, an
OSAn operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
bootedIn computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...
from a write-locked SD card is robust, rugged, reliable, and impervious to permanent corruption. If the running OS degrades, simply turning the machine off and then on returns it back to its initial virgin uncorrupted state and thus is particularly solid. The SD card installed OS does not require removal of corrupted components since it was write-locked though any written media may need to be restored.
In 2011 Intel introduced a caching mechanism for their Z68 chipset (and mobile derivatives) called
Smart Response TechnologyIn computing, Smart Response Technology is a proprietary caching mechanism introduced in 2011 by Intel for their Z68 chipset , which allows a SATA solid-state drive to function as cache for a hard disk drive.SRT is implemented in the device driver and firmware...
, which allows a
SATASata is a traditional dish from the Malaysian state of Terengganu, consisting of spiced fish meat wrapped in banana leaves and cooked on a grill.It is a type of Malaysian fish cake, or otak-otak...
SSD to be used as a
cacheIn computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...
(configurable as write-through or write-back) for a conventional, magnetic hard disk drive. A similar technology is available on
HighPointHighpoint can refer to:*Highpoint, Florida, an unincorporated community near Tampa Bay*Highpoint Center for Printmaking, a print workshop in Minneapolis*Highpoint Shopping Centre in Melbourne, Australia*Highpoint I, a set of apartment buildings in London...
's RocketHybrid PCIe card.
Hybrid driveA Hybrid Drive, Hybrid Hard Drive , or Hybrid Hard Disk Drive is a type of large-buffer computer hard disk drive. It is different from standard hard drives in that it integrates a cache using non-volatile memory or even a small solid-state drive...
s (H-HDSs) are based on the same principle, but integrate some amount of flash memory on board of a conventional drive instead of using a separate SSD. The flash layer in these drives can be accessed independently from the
magnetic storageMagnetic storage and magnetic recording are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using...
by the host using ATA-8 commands, allowing the operating system to manage it. For example Microsoft's ReadyDrive technology explicitly stores portions of the hibernation file in the cache of these drives when the system hibernates, making the subsequent resume faster.
SSD-optimized file systems
There are a number of computer
file systemA file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
s which are optimized for solid-state drives. Some of the more popular or notable are listed below.
Microsoft Windows
Versions of
WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
prior to Windows 7 are optimized for hard disk drives rather than SSDs.
Windows VistaWindows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
includes
ReadyBoostReadyBoost is a disk cache component of Microsoft Windows, first introduced with Microsoft's Windows Vista in 2006 and bundled with Windows 7 in 2009...
to exploit characteristics of USB-connected flash devices, but for SSDs it only improves the default partition alignment to prevent read-modify-write operations which reduce the speed of the SSD. This is because most SSDs are typically aligned on 4 KB sectors and most OSes are based on 512 byte sectors with the default partition set up unaligned . The proper alignment really does not help the SSD's endurance over the life of the drive, however some Vista operations, if not disabled, can shorten the life of the SSD. Disk
defragmentationIn the maintenance of file systems, defragmentation is a process that reduces the amount of fragmentation. It does this by physically organizing the contents of the mass storage device used to store files into the smallest number of contiguous regions . It also attempts to create larger regions of...
should be disabled because the location of the file components on an SSD doesn't significantly impact its performance, but moving the files to make them contiguous using the Windows Defrag routine will cause unnecessary write wear on the limited number of P/E cycles on the SSD. The Superfetch feature will not materially improve the performance of the system and causes additional overhead in the system and SSD, although it does not cause wear.
Windows 7 is optimized for SSDs as well as for traditional magnetic hard disks. The OS looks for the presence of an SSD and operates differently with that drive. If an SSD is present, Windows 7 will disable disk defragmentation, Superfetch, ReadyBoost, and other boot-time and application prefetching operations. It also includes support for the
TRIMIn computing, a TRIM command allows an operating system to inform a solid-state drive which blocks of data are no longer considered in use and can be wiped internally. While TRIM is frequently spelled in capital letters, it is not an acronym; it is merely a command name.TRIM was introduced soon...
command to reduce garbage collection of data which the OS has already determined is no longer valid. Without support for TRIM, the SSD would be unaware of this data being invalid and would unnecessarily continue to rewrite this data during garbage collection causing further wear on the SSD.
ZFS
Solaris as of version 10 Update 6 (released in October 2008), and recent versions of
OpenSolarisOpenSolaris was an open source computer operating system based on Solaris created by Sun Microsystems. It was also the name of the project initiated by Sun to build a developer and user community around the software...
and Solaris Express Community Edition can use SSDs as a performance booster for
ZFSIn computing, ZFS is a combined file system and logical volume manager designed by Sun Microsystems. The features of ZFS include data integrity verification against data corruption modes , support for high storage capacities, integration of the concepts of filesystem and volume management,...
. A low-latency SSD can be used for the ZFS Intent Log (ZIL), where it is named the SLOG. This is used every time a synchronous write to the disk occurs. An SSD (not necessarily with a low-latency) may also be used for the level 2
Adaptive Replacement CacheAdaptive Replacement Cache is a page replacement algorithm withbetter performance than LRU developed at the IBM Almaden Research Center. This is accomplished by keeping track of both Frequently Used and Recently Used pages plus a recent eviction history for both...
(L2ARC), which is used to cache data for reading. When used either alone or in combination, large increases in performance are generally seen.
FreeBSD
In addition to ZFS features described above,
UFSThe Unix file system is a file system used by many Unix and Unix-like operating systems. It is also called the Berkeley Fast File System, the BSD Fast File System or FFS...
supports the
TRIMIn computing, a TRIM command allows an operating system to inform a solid-state drive which blocks of data are no longer considered in use and can be wiped internally. While TRIM is frequently spelled in capital letters, it is not an acronym; it is merely a command name.TRIM was introduced soon...
command.
Linux systems
The Linux kernel supports the TRIM function starting with version 2.6.33. The
ext4The ext4 or fourth extended filesystem is a journaling file system for Linux, developed as the successor to ext3.It was born as a series of backward compatible extensions to ext3, many of them originally developed by Cluster File Systems for the Lustre file system between 2003 and 2006, meant to...
file system is supported when mounted using the "discard" parameter. The most recent disk utilities (and therefore installation software that make use of them) also apply proper partition alignment.
Mac OS X
Mac OS X 10.7 (Lion) supports TRIM, as does OS X 10.6.8 Snow Leopard. It is possible to add TRIM to versions earlier than 10.6.8.
Standardization organizations
The following are noted standardization organizations and bodies that work to create standards for solid-state drives (and other computer storage devices). It also includes organizations who promote the use of solid-state drives. This is not necessarily an exhaustive list.
| Organization or Committee |
Subcommittee of: |
Purpose |
| INCITS |
N/A |
Coordinates technical standards activity between ANSI in the USA and joint ISO/IEC committees worldwide |
| T10 |
INCITS |
SCSI Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
|
| T11 |
INCITS |
FCFibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
|
| T13 |
INCITS |
ATAParallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...
|
| JEDEC The JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...
|
N/A |
Develops open standards and publications for the microelectronics industry |
| JC-64.8 The JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...
|
JEDEC |
Focuses on solid-state drive standards and publications |
| NVMHCI |
N/A |
Provides standard software and hardware programming interfaces for nonvolatile memory subsystems |
| SATA-IO Serial ATA International Organization is an independent, non-profit organization which provides the computing industry with guidance and support for implementing the SATA specification. SATA-IO was developed by and for leading industry companies...
|
N/A |
Provides the industry with guidance and support for implementing the SATA specification |
| SFF Committee The Small Form Factor committee is an ad hoc electronics industry group formed to quickly develop interoperability specifications ....
|
N/A |
Works on storage industry standards needing prompt attention when not addressed by other standards committees |
| SNIA An association of producers and consumers of storage networking products, whose goal is to further storage networking technology and applications.The Storage Networking Industry Association, or SNIA, was incorporated in December, 1997, and is a registered 501 non-profit trade association...
|
N/A |
Develops and promotes standards, technologies, and educational services in the management of information |
| SSSI |
SNIA |
Fosters the growth and success of solid state storage |
A
solid-state drive (SSD), sometimes called a
solid-state disk or
electronic disk, is a
data storage devicethumb|200px|right|A reel-to-reel tape recorder .The magnetic tape is a data storage medium. The recorder is data storage equipment using a portable medium to store the data....
that uses solid-state
memoryComputer data storage, often called storage or memory, refers to computer components and recording media that retain digital data. Data storage is one of the core functions and fundamental components of computers....
to store
persistent dataPersistence in computer science refers to the characteristic of state that outlives the process that created it. Without this capability, state would only exist in RAM, and would be lost when this RAM loses power, such as a computer shutdown....
with the intention of providing access in the same manner of a traditional block i/o hard disk drive. SSDs are distinguished from traditional magnetic disks such as hard disk drives (HDDs) or
floppy diskA floppy disk is a disk storage medium composed of a disk of thin and flexible magnetic storage medium, sealed in a rectangular plastic carrier lined with fabric that removes dust particles...
, which are electromechanical devices containing spinning
disksDisk storage or disc storage is a general category of storage mechanisms, in which data are digitally recorded by various electronic, magnetic, optical, or mechanical methods on a surface layer deposited of one or more planar, round and rotating disks...
and movable
read/write headsDisk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...
. In contrast, SSDs use
microchipAn integrated circuit or monolithic integrated circuit is an electronic circuit manufactured by the patterned diffusion of trace elements into the surface of a thin substrate of semiconductor material...
s that retain data in non-volatile memory chips and contain no
moving partsThe moving parts of a machine are those parts of it that move. Machines comprise both moving and fixed parts. The moving parts have controlled and constrained motions....
. Compared to electromechanical HDDs, SSDs are typically less susceptible to physical shock, are silent, have lower
access timeAccess time is the time delay or latency between a request to an electronic system, and the access being completed or the requested data returned....
and
latencyLatency is a measure of time delay experienced in a system, the precise definition of which depends on the system and the time being measured. Latencies may have different meaning in different contexts.-Packet-switched networks:...
, but are more expensive per
gigabyteThe gigabyte is a multiple of the unit byte for digital information storage. The prefix giga means 109 in the International System of Units , therefore 1 gigabyte is...
(GB). SSDs use the same interface as hard disk drives, thus easily replacing them in most applications.
, most SSDs use NAND-based flash memory, which retains memory even without power. SSDs using volatile
random-access memoryRandom access memory is a form of computer data storage. Today, it takes the form of integrated circuits that allow stored data to be accessed in any order with a worst case performance of constant time. Strictly speaking, modern types of DRAM are therefore not random access, as data is read in...
(RAM) also exist for situations that require even faster access, but do not necessarily need data
persistencePersistence in computer science refers to the characteristic of state that outlives the process that created it. Without this capability, state would only exist in RAM, and would be lost when this RAM loses power, such as a computer shutdown....
after power loss, or use external power or batteries to maintain the data after power is removed.
A
hybrid driveA Hybrid Drive, Hybrid Hard Drive , or Hybrid Hard Disk Drive is a type of large-buffer computer hard disk drive. It is different from standard hard drives in that it integrates a cache using non-volatile memory or even a small solid-state drive...
combines the features of an HDD and an SSD into one unit, containing a large HDD and a smaller SSD cache to improve performance of frequently accessed files. These can offer near-SSD performance in most applications (such as system startup and loading applications) at a lower price than an SSD. These are not suitable for data-intensive work, nor do they offer the other advantages of SSDs.
Development and history
Early SSDs using RAM and similar technology
The origins of SSDs came from the 1950s using two similar technologies,
magnetic core memoryMagnetic-core memory was the predominant form of random-access computer memory for 20 years . It uses tiny magnetic toroids , the cores, through which wires are threaded to write and read information. Each core represents one bit of information...
and card capacitor read-only store (CCROS). These auxiliary memory units, as they were called at the time, emerged during the era of
vacuum tubeIn electronics, a vacuum tube, electron tube , or thermionic valve , reduced to simply "tube" or "valve" in everyday parlance, is a device that relies on the flow of electric current through a vacuum...
computers. But with the introduction of cheaper
drum storage unitsDrum memory is a magnetic data storage device and was an early form of computer memory widely used in the 1950s and into the 1960s, invented by Gustav Tauschek in 1932 in Austria....
, their use was discontinued.
Later, in the 1970s and 1980s, SSDs were implemented in semiconductor memory for early supercomputers of
IBMInternational Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
,
AmdahlAmdahl Corporation is an information technology company which specializes in IBM mainframe-compatible computer products. Founded in 1970 by Dr. Gene Amdahl, a former IBM employee, it has been a wholly owned subsidiary of Fujitsu since 1997...
and
CrayCray Inc. is an American supercomputer manufacturer based in Seattle, Washington. The company's predecessor, Cray Research, Inc. , was founded in 1972 by computer designer Seymour Cray. Seymour Cray went on to form the spin-off Cray Computer Corporation , in 1989, which went bankrupt in 1995,...
; however, the prohibitively high price of the built-to-order SSDs made them quite seldom used. In the late 1970s, General Instruments produced an electrically alterable ROM (EAROM) which operated somewhat like the later NAND flash memory, but the inability to achieve a 10-year life was not practical and many companies abandoned the technology. In 1976
DataramDataram Corporation is an international manufacturer of computer memory, storage, and software products, founded in 1967 as a supplier of original equipment memory to Digital Equipment Corporation.-Company overview:...
started selling a product called
BULK CORE providing up to 2MB of solid state storage compatible with
DECDigital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
and
Data GeneralData General was one of the first minicomputer firms from the late 1960s. Three of the four founders were former employees of Digital Equipment Corporation. Their first product, the Data General Nova, was a 16-bit minicomputer...
computers.
Texas Memory SystemsTexas Memory Systems, Inc. is a privately held American corporation that designs and manufacturers solid-state disks and digital signal processors . TMS was founded in 1978 and that same year introduced their first solid-state drive, followed by their first digital signal processor...
introduced a 16
kilobyteThe kilobyte is a multiple of the unit byte for digital information. Although the prefix kilo- means 1000, the term kilobyte and symbol KB have historically been used to refer to either 1024 bytes or 1000 bytes, dependent upon context, in the fields of computer science and information...
(KB) RAM solid-state drive in 1978 to be used by oil companies for
seismic dataReflection seismology is a method of exploration geophysics that uses the principles of seismology to estimate the properties of the Earth's subsurface from reflected seismic waves. The method requires a controlled seismic source of energy, such as dynamite/Tovex, a specialized air gun or a...
acquisition. The following year, StorageTek developed the first modern type of solid-state drive.
The
Sharp PC-5000The Sharp PC-5000 was a pioneering laptop computer, announced by Sharp Corporation of Japan in 1983. Like the GRiD Compass, which preceded it, and its contemporary the Gavilan SC, it employed a clamshell design in which the display closes over the keyboard....
, introduced in 1983, used 128 kilobyte solid-state storage cartridges, containing
bubble memoryBubble memory is a type of non-volatile computer memory that uses a thin film of a magnetic material to hold small magnetized areas, known as bubbles or domains, each storing one bit of data...
. In 1984 Tallgrass Technologies Corporation had a tape back up unit of 40 MB with a solid state 20 MB unit built in. The 20 MB unit could be used instead of a hard drive. In September 1986, Santa Clara Systems introduced BatRam, 4
megabyteThe megabyte is a multiple of the unit byte for digital information storage or transmission with two different values depending on context: bytes generally for computer memory; and one million bytes generally for computer storage. The IEEE Standards Board has decided that "Mega will mean 1 000...
(MB) mass storage system expandable to 20 MB using 4 MB memory modules. The package included a rechargeable battery to preserve the memory chip contents when the array was not powered. 1987 saw the entry of
EMC CorporationEMC Corporation , a Financial Times Global 500, Fortune 500 and S&P 500 company, develops, delivers and supports information infrastructure and virtual infrastructure hardware, software, and services. EMC is headquartered in Hopkinton, Massachusetts, USA.Former Intel executive Richard Egan and his...
into the SSD market, with drives introduced for the mini-computer market. However, by 1993 EMC had exited the SSD market.
Software-based
RAM DiskA RAM disk or RAM drive is a block of RAM that a computer's software is treating as if the memory were a disk drive...
s are still used today because they are an
order of magnitudeAn order of magnitude is the class of scale or magnitude of any amount, where each class contains values of a fixed ratio to the class preceding it. In its most common usage, the amount being scaled is 10 and the scale is the exponent being applied to this amount...
faster than the fastest SSD, but they consume CPU resources and cost much more on a per GB basis.
Flash-based SSDs
In 1994,
STEC, Inc.STEC, Inc. is a multinational company and a leader in enterprise solid-state drive .The company is headquartered in Santa Ana, California...
bought Cirrus Logic’s flash controller operation, allowing the company to enter the flash memory business for consumer electronic devices.
In 1995,
M-SystemsM-Systems Ltd., was a Nasdaq-listed Israeli producer of Flash memory storage products founded in 1989 by Dov Moran and based in Kfar Sava, Israel. They were best known for developing and patenting the first flash drive, marketed in 1995 as DiskOnChip, and the first USB flash drive, marketed in...
introduced flash-based solid-state drives. They had the advantage of not requiring batteries to maintain the data in the memory (required by the prior volatile memory systems), but were not as fast as the DRAM-based solutions. Since then, SSDs have been used successfully as HDD replacements by the military and aerospace industries, as well as for other mission-critical applications. These applications require the exceptional mean time between failures (MTBF) rates that solid-state drives achieve, by virtue of their ability to withstand extreme shock, vibration and temperature ranges.
BiTMICRO made a number of introductions and announcements in 1999 around flash-based SSDs including an 18 GB 3.5 in SSD. Fusion-io announced a PCIe-based SSD with 100,000
input/output operations per secondIOPS is a common performance measurement used to benchmark computer storage devices like hard disk drives , solid state drives , and storage area networks...
(IOPS) of performance in a single card with capacities up to 320 gigabytes in 2007. At Cebit 2009, OCZ demonstrated a 1
terabyteThe terabyte is a multiple of the unit byte for digital information. The prefix tera means 1012 in the International System of Units , and therefore 1 terabyte is , or 1 trillion bytes, or 1000 gigabytes. 1 terabyte in binary prefixes is 0.9095 tebibytes, or 931.32 gibibytes...
(TB) flash SSD using a PCI Express ×8 interface. It achieves a maximum write speed of 654 megabytes per second (MB/s) and maximum read speed of 712 MB/s. In December 2009,
Micron TechnologyMicron Technology, Inc. is an American multinational corporation based in Boise, Idaho, USA, best known for producing many forms of semiconductor devices. This includes DRAM, SDRAM, flash memory, SSD and CMOS image sensing chips. Consumers may be more familiar with its consumer brand Crucial...
announced the world's first SSD using a 6 gigabits per second (Gbit/s) or 600 (MB/s)
SATASata is a traditional dish from the Malaysian state of Terengganu, consisting of spiced fish meat wrapped in banana leaves and cooked on a grill.It is a type of Malaysian fish cake, or otak-otak...
interface.
Enterprise flash drives
Enterprise flash drives (EFDs) are designed for applications requiring high I/O performance (
IOPSIOPS is a common performance measurement used to benchmark computer storage devices like hard disk drives , solid state drives , and storage area networks...
), reliability, and energy efficiency. In most cases an EFD is an SSD with a higher set of specifications compared to SSDs that would typically be used in notebook computers. The term was first used by EMC in January 2008, to help them identify SSD manufacturers who would provide products meeting these higher standards. There are no standards bodies who control the definition of EFDs, so any SSD manufacturer may claim to produce EFDs when they may not actually meet the requirements. Likewise there may be other SSD manufacturers that meet the EFD requirements without being called EFDs.
Architecture and function
The key components of an SSD are the controller and the memory to store the data. The primary memory component in an SSD had been
DRAMDram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...
volatile memoryVolatile memory, also known as volatile storage, is computer memory that requires power to maintain the stored information, unlike non-volatile memory which does not require a maintained power supply...
since they were first developed, but since 2009 it is more commonly NAND flash
non-volatile memoryNon-volatile memory, nonvolatile memory, NVM or non-volatile storage, in the most basic sense, is computer memory that can retain the stored information even when not powered. Examples of non-volatile memory include read-only memory, flash memory, ferroelectric RAM, most types of magnetic computer...
. Other components play a less significant role in the operation of the SSD and vary between manufacturers.
Controller
Every SSD includes a
controllerA flash memory controller manages the data stored on flash memory and communicates with a computer or electronic device. Flash memory controllers can be designed for operating in low duty-cycle environments like SD cards, CompactFlash cards, or other similar media for use in digital cameras, PDAs,...
that incorporates the electronics that bridge the NAND memory components to the host
computerA computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
. The controller is an embedded processor that executes firmware-level code and is one of the most important factors of SSD performance. Some of the functions performed by the controller include:
- Error correction (ECC)
- Wear leveling
Wear leveling is a technique for prolonging the service life of some kinds of erasable computer storage media, such as Flash memory used in solid-state drives and USB Flash drives...
- Bad block
Bad Sector is an ambient/noise project formed in 1992 in Tuscany, Italy by Massimo Magrini. While working at the Computer Art Lab of ISTI in Pisa , he developed original gesture interfaces that he uses in live performances: 'Aerial Painting Hand' , 'UV-Stick' Bad Sector is an ambient/noise...
mapping
- Read scrubbing
Memory scrubbing is the process of detecting and correcting bit errors in computer memory by using error-detecting codes like ECC.-Motivation for scrubbing:...
and read disturb management
- Read and write caching
In computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...
- Garbage collection
- Encryption
In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...
The performance of the SSD can scale with the number of parallel NAND flash chips used in the device. A single NAND chip is relatively slow, due to narrow (8/16 bit) asynchronous IO interface, and additional high latency of basic IO operations (typical for SLC NAND, ~25
μsA microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
to fetch a 4K page from the array to the IO buffer on a read, ~250 μs to commit a 4K page from the IO buffer to the array on a write, ~2 ms to erase a 256 kiB block). When multiple NAND devices operate in parallel inside an SSD, the bandwidth scales, and the high latencies can be hidden, as long as enough outstanding operations are pending and the load is evenly distributed between devices. Micron and Intel initially made faster SSDs by implementing
data stripingIn computer data storage, data striping is the technique of segmenting logically sequential data, such as a file, in a way that accesses of sequential segments are made to different physical storage devices. Striping is useful when a processing device requests access to data more quickly than a...
(similar to
RAIDRAID is a storage technology that combines multiple disk drive components into a logical unit...
0) and interleaving in their architecture. This enabled the creation of ultra-fast SSDs with 250 MB/s effective read/write speeds with the SATA 3 Gb/s interface in 2009. Two years later and continuing to leverage this parallel flash connectivity, SandForce released consumer-grade SATA 6 Gb/s SSD controllers which support 500 MB/s read/write speeds.
Flash memory-based
Most SSD manufacturers use
non-volatile NAND flash memoryFlash memory is a non-volatile computer storage chip that can be electrically erased and reprogrammed. It was developed from EEPROM and must be erased in fairly large blocks before these can be rewritten with new data...
in the construction of their SSDs because of the lower cost compared to
DRAMDram or DRAM may refer to:As a unit of measure:* Dram , an imperial unit of mass and volume* Armenian dram, a monetary unit* Dirham, a unit of currency in several Arab nationsOther uses:...
. and the ability to retain the data without a constant power supply, ensuring data persistence through sudden power outages. Flash memory SSDs are slower than DRAM solutions, and some early designs were even slower than HDDs after continued use. This problem was resolved by controllers that came out in 2009 and later.
Flash memory-based solutions are typically packaged in standard disk drive form factors (1.8-, 2.5-, and 3.5-inch), or smaller unique and compact layouts because of the compact memory.
Lower priced drives usually use
multi-level cellIn electronics, a multi-level cell is a memory element capable of storing more than a single bit of information.MLC NAND flash is a flash memory technology using multiple levels per cell to allow more bits to be stored using the same number of transistors...
(MLC) flash memory, which is slower and less reliable than single-level cell (SLC) flash memory. This can be mitigated or even reversed by the internal design structure of the SSD, such as interleaving, changes to writing algorithms, and higher over-provisioning (more excess capacity) with which the wear-leveling algorithms can work.
DRAM-based
SSDs based on volatile memory such as DRAM are characterized by ultrafast data access, generally less than 10
microsecondA microsecond is an SI unit of time equal to one millionth of a second. Its symbol is µs.A microsecond is equal to 1000 nanoseconds or 1/1000 millisecond...
s, and are used primarily to accelerate applications that would otherwise be held back by the latency of flash SSDs or traditional HDDs. DRAM-based SSDs usually incorporate either an internal battery or an external AC/DC adapter and
backupIn information technology, a backup or the process of backing up is making copies of data which may be used to restore the original after a data loss event. The verb form is back up in two words, whereas the noun is backup....
storage systems to ensure data persistence while no power is being supplied to the drive from external sources. If power is lost, the battery provides power while all information is copied from random access memory (RAM) to back-up storage. When the power is restored, the information is copied back to the RAM from the back-up storage, and the SSD resumes normal operation (similar to the
hibernateHibernation in computing is powering down a computer while retaining its state.Upon hibernation, the computer saves the contents of its random access memory to a hard disk or other non-volatile storage...
function used in modern operating systems).
SSDs of this type are usually fitted with DRAM modules of the same type used in regular PCs and servers, which can be swapped out and replaced by larger modules.
A
remote, indirect memory-access disk (RIndMA Disk) uses a secondary computer with a fast network or (direct)
InfinibandInfiniBand is a switched fabric communications link used in high-performance computing and enterprise data centers. Its features include high throughput, low latency, quality of service and failover, and it is designed to be scalable...
connection to act like a RAM-based SSD, but the new faster flash memory based SSDs already available in 2009 are making this option not as cost effective.
Cache or buffer
A flash-based SSD typically uses a small amount of DRAM as a cache, similar to the cache in Hard disk drives. A directory of block placement and wear leveling data is also kept in the cache while the drive is operating. Data is not permanently stored in the cache. One SSD controller manufacturer,
SandForceSandForce is an American "fabless" semiconductor company based in Milpitas, California, that designs and manufactures flash memory controllers for solid-state drives . On October 26th 2011 it was acquired by LSI Corporation....
, does not use an external DRAM cache on their designs, but still achieve very high performance. Eliminating the external DRAM enables a smaller footprint for the other flash memory components in order to build even smaller SSDs.
Battery or super capacitor
Another component in higher performing SSDs is a capacitor or some form of battery. These are necessary to maintain data integrity such that the data in the cache can be flushed to the drive when power is dropped; some may even hold power long enough to maintain data in the cache until power is resumed. In the case of MLC flash memory, a problem called
lower page corruption can occur when MLC flash memory loses power while programming an upper page. The result is data written previously and presumed safe can be corrupted if the memory is not supported by a super capacitor in the event of a sudden power loss. This problem does not exist with SLC flash memory.
Host interface
The host interface is not specifically a component of the SSD, but it is a key part of the drive. The interface is usually incorporated into the controller discussed above. The interface is generally one of the interfaces found in HDDs. They include:
- Serial ATA
Serial ATA is a computer bus interface for connecting host bus adapters to mass storage devices such as hard disk drives and optical drives...
- Serial attached SCSI
Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,...
(generally found on serversIn the context of client-server architecture, a server is a computer program running to serve the requests of other programs, the "clients". Thus, the "server" performs some computational task on behalf of "clients"...
)
- PCI Express
PCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...
- Fibre Channel
Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
(almost exclusively found on servers)
- USB
- Parallel ATA
Parallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...
(IDEParallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...
) interface (mostly replaced by SATA)
- (Parallel) SCSI
Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
(generally found on servers; mostly replaced by SAS; last SCSI-based SSD introduced in 2004)
Form factor
The size and shape of any device is largely driven by the size and shape of the components used to make that device. Traditional HDDs and optical drives are designed around the rotating platter or
optical discIn computing and optical disc recording technologies, an optical disc is a flat, usually circular disc which encodes binary data in the form of pits and lands on a special material on one of its flat surfaces...
along with the spindle motor inside. If an SSD is made up of various interconnected integrated circuits (ICs) and an interface connector, then its shape could be virtually anything imaginable because it is no longer limited to the shape of rotating media drives. Some solid state storage solutions come in a larger chassis that may even be a rack-mount form factor with numerous SSDs inside. They would all connect to a common bus inside the chassis and connect outside the box with a single connector.
Standard HDD form factors
The benefit of using a current HDD form factor would be to take advantage of the extensive infrastructure already in place to mount and connect the drives to the host system. These traditional form factors are known by the size of the rotating media, e.g., 5.25", 3.5", 2.5", 1.8", not by the dimensions of the drive casing.
Box form factors
Many of the DRAM-based solutions use a box that is often designed to fit in a rack-mount system. The number of DRAM components required to get sufficient capacity to store the data along with the backup power supplies requires a larger space than traditional HDD form factors.
Bare-board form factors
Form factors which were more common to memory modules are now being used by SSDs to take advantage of their flexibility in laying out the components. Some of these include
PCIePCI Express , officially abbreviated as PCIe, is a computer expansion card standard designed to replace the older PCI, PCI-X, and AGP bus standards...
, mini PCIe, mini-DIMM, MO-297, and many more. The SATADIMM from Viking Modular uses an empty DDR3 DIMM slot on the motherboard to provide power to the drive with a separate SATA connector to provide the data connection back to the computer. The result is an easy to install SSD with a capacity equal to drives that typically take a full 2.5 in expansion slot. At least one manufacturer, InnoDisk, is producing a drive that sits directly on the SATA connector on the motherboard without any other support or mechanical mount. Some SSDs are based on the PCIe form factor and connect both the data interface and power through the PCIe connector to the host. These drives can use either direct PCIe flash controllers or a PCIe-to-SATA bridge device which then connects to SATA flash controller(s).
Ball grid array form factors
In the early 2000s, a few companies introduced SSDs in
Ball Grid ArrayA ball grid array is a type of surface-mount packaging used for integrated circuits.- Description :The BGA is descended from the pin grid array , which is a package with one face covered with pins in a grid pattern. These pins conduct electrical signals from the integrated circuit to the printed...
(BGA) form factors, such as M-Systems’ (now
SanDiskSanDisk Corporation is an American multinational corporation that designs, develops and manufactures data storage solutions in a range of form factors using the flash memory, controller and firmware technologies. It was founded in 1988 by Dr. Eli Harari and Sanjay Mehrotra, non-volatile memory...
) DiskOnChip and
Silicon Storage TechnologySilicon Storage Technology, Inc. is a Sunnyvale, California, USA, technology company producing non-volatile memory devices and related products.It was founded by Bing Yeh in 1989....
’s NANDrive (now produced by
Greenliant SystemsGreenliant Systems is a manufacturer of flash memory, solid-state storage and controller semiconductors for embedded system, data center and mobile products. Greenliant was founded in 2010, when former Silicon Storage Technology CEO Bing Yeh acquired several flash memory assets from the company...
), and
MemorightMemoright is a Taiwan based storage products house founded in March 2006.It produced a 2.5inch SSD with a claimed read/write speed of 100mb/s, the fastest SSD available at the time....
's M1000 for use in embedded systems. The main benefits of BGA SSDs are their low power consumption, small chip package size to fit into compact subsystems, and that they can be soldered directly onto a system motherboard to reduce adverse effects from vibration and shock.
Comparison of SSD with hard disk drives
Making a comparison between SSDs and ordinary (spinning) HDDs is difficult. Traditional HDD
benchmarksIn computing, a benchmark is the act of running a computer program, a set of programs, or other operations, in order to assess the relative performance of an object, normally by running a number of standard tests and trials against it...
are focused on finding the performance aspects where they are weak, such as rotational latency time and seek time. As SSDs do not spin, or seek, they may show huge superiority in such tests. However, SSDs have challenges with mixed reads and writes, and their performance may degrade over time. SSD testing must start from the (in use) full disk, as the new and empty (fresh out of the box) disk may have much better write performance than it would show after only weeks of use.
Comparisons reflect typical characteristics, and may not hold for a specific device.
| Attribute or characteristic |
Solid-state drive |
Hard disk drive |
| Spin-up Spin-up refers to the process of a traditional hard disk drive accelerating its platters from a stopped state to an operational speed. The period of time taken by the drive to perform this process is referred to as its spin-up time, the average of which is a S.M.A.R.T. attribute. The required...
time |
Almost Instantaneous; nothing mechanical to "spin up". May need a few milliseconds to come out of an automatic power-saving mode. |
May take several seconds. With a large number of drives, spin-up may need to be staggered to limit total power drawn. |
| Random access In computer science, random access is the ability to access an element at an arbitrary position in a sequence in equal time, independent of sequence size. The position is arbitrary in the sense that it is unpredictable, thus the use of the term "random" in "random access"...
time |
About 0.1 ms - many times faster than HDDs because data is accessed directly from the flash memory |
Ranges from 5–10 ms due to the need to move the heads and wait for the data to rotate under the read/write head Disk read/write heads are the small parts of a disk drive, that move above the disk platter and transform platter's magnetic field into electrical current or vice versa – transform electrical current into magnetic field...
|
| Read latency time |
Generally low because the data can be read directly from any location; In applications where hard disk seeks are the limiting factor, this results in faster boot and application launch times (see Amdahl's law Amdahl's law, also known as Amdahl's argument, is named after computer architect Gene Amdahl, and is used to find the maximum expected improvement to an overall system when only part of the system is improved...
). |
Generally high since the mechanical components require additional time to get aligned |
| Consistent read performance |
Read performance does not change based on where data is stored on an SSD |
If data is written in a fragmented way, reading back the data will have varying response times |
DefragmentationIn the maintenance of file systems, defragmentation is a process that reduces the amount of fragmentation. It does this by physically organizing the contents of the mass storage device used to store files into the smallest number of contiguous regions . It also attempts to create larger regions of...
|
SSDs do not benefit from defragmentation because there is little benefit to reading data sequentially (beyond typical FS block sizes) and any defragmentation process adds additional writes on the NAND flash that already have a limited cycle life. |
HDDs may require defragmentation after continued operations or erasing and writing data, especially involving large files . |
AcousticAcoustics is the interdisciplinary science that deals with the study of all mechanical waves in gases, liquids, and solids including vibration, sound, ultrasound and infrasound. A scientist who works in the field of acoustics is an acoustician while someone working in the field of acoustics...
levels |
SSDs have no moving parts and make no sound |
HDDs have moving parts (heads, spindle motor) and have varying levels of sound depending upon model |
Mechanical reliabilityReliability engineering is an engineering field, that deals with the study, evaluation, and life-cycle management of reliability: the ability of a system or component to perform its required functions under stated conditions for a specified period of time. It is often measured as a probability of...
|
A lack of moving parts virtually eliminates mechanical breakdowns |
HDDs have many moving parts that are all subject to failure over time |
| Susceptibility to environmental factors |
No flying heads or rotating platters to fail as a result of shock, altitude, or vibration |
The flying heads and rotating platters are generally susceptible to shock, altitude, and vibration |
| Magnetic Magnetic storage and magnetic recording are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using...
susceptibility |
No impact on flash memory |
Magnets or magnetic surges can alter data on the media |
| Weight and size |
The weight of flash memory and the circuit board material are very light compared to HDDs |
Higher performing HDDs require heavier components than laptop HDDs (which are light, but not as light as SSDs) |
| Parallel operation |
Some flash controllers can have multiple flash chips reading and writing different data simultaneously |
HDDs have multiple heads (one per platter) but they are connected, and share one positioning motor. |
| Write longevity |
Flash-based SSDs have a limited number of writes (1-5 million or more) over the life of the drive. Software controllers manage this limitation in such a way that drives can last for many decades before failure. SSDs based on DRAM do not have a limited number of writes. |
Magnetic media do not have a similar limited number of writes but are susceptible to eventual mechanical failure. |
| Software encryption limitations |
NAND flash memory cannot be overwritten, but has to be rewritten to previously erased blocks. If a software encryption In cryptography, encryption is the process of transforming information using an algorithm to make it unreadable to anyone except those possessing special knowledge, usually referred to as a key. The result of the process is encrypted information...
program encrypts data already on the SSD, the overwritten data is still unsecured, unencrypted, and accessible (drive-based hardware encryption does not have this problem). Also data cannot be securely erased by overwriting the original file without special "Secure Erase" procedures built into the drive. |
HDDs can overwrite data directly on the drive in any particular sector. |
| Cost per capacity |
, NAND flash SSDs cost about (US)$.90–2.00 per GB |
, HDDs cost about (US)$0.05/GB for 3.5 in and $0.10/GB for 2.5 in drives |
| Storage capacity |
, SSDs come in different sizes up to 2TB but are typically not larger than 64-256GB, due to their high cost per GB. |
, HDDs are typically 500GB-1TB but drives as large as 2 or 3 TB are also available. |
| Read/write performance symmetry |
Less expensive SSDs typically have write speeds significantly lower than their read speeds. Higher performing SSDs have a balanced read and write speed. |
HDDs generally have slightly lower write speeds than their read speeds. |
| Free block availability and TRIM Trim may refer to:* Cutting small pieces off something** Book trimming, a stage of the publishing process** Editing*** Editing a posting style in online discourse** Pruning, trimming as a form of pruning often used on trees-Places:...
|
SSD write performance is significantly impacted by the availability of free, programmable blocks. Previously written data blocks that are no longer in use can be reclaimed by TRIM; however, even with TRIM, fewer free, programmable blocks translates into reduced performance. |
HDDs are not affected by free blocks or the operation (or lack) of the TRIM command |
| Power consumption |
High performance flash-based SSDs generally require 1/2 to 1/3 the power of HDDs; High performance DRAM SSDs generally require as much power as HDDs and consume power when the rest of the system is shut down. |
High performance HDDs generally require between 12-18 watts; drives designed for notebook computers are typically 2 watts. |
Comparison of SSD with memory cards
While it is true that both memory cards and most SSDs use flash memory, they serve very different markets and purposes. Each has a number of different attributes which are optimized and adjusted to best meet the needs of particular users. Some of these characteristics include power consumption, performance, size, and reliability.
SSDs were originally designed for use in a computer system. The first units were intended to replace or augment hard disk drives, so the operating system recognized them as a hard drive. Originally, solid state drives were even shaped and mounted in the computer like hard drives. Later SSDs became smaller and more compact, eventually developing their own unique form factors. The SSD was designed to be installed one time inside the computer and only have it removed when servicing or upgrading it.
In contrast, memory cards like
CompactFlashCompactFlash is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994...
(CF),
Secure DigitalSecure Digital is a non-volatile memory card format developed by the SD Card Association for use in portable devices. The SD technology is used by more than 400 brands across dozens of product categories and more than 8,000 models, and is considered the de-facto industry standard.Secure Digital...
(SD), Memory Stick, and xD-Picture Card were all originally designed for digital cameras and later found their way into cell phones, gaming devices, and GPS units. Nearly all memory cards are smaller in size than SSDs and they were engineered to be inserted and removed repeatedly. There are adapters which enable some memory cards like the CF card to interface to a computer as an SSD, but they are not intended to be the primary storage device in the computer. The typical CF card interface is generally 3-4 times slower than is available on SSDs.
Commercialization
Cost and capacity
The technological trend of
2 yearMoore's law describes a long-term trend in the history of computing hardware: the number of transistors that can be placed inexpensively on an integrated circuit doubles approximately every two years....
50% decline in costs is no longer possible in NAND flash as it approaches its terminal node. Instead NAND makers anticipate more modest cost declines in the period 2011-2015. Capacities in client SSDs are typically dictated by cost concerns rather than technical limitations of NAND storage.
Availability
Solid-state drive (SSD) technology has been marketed to the military and niche industrial markets since the mid-1990s..
Along with the emerging enterprise market, SSDs have been appearing in ultra-mobile PCs and a few lightweight laptop systems, adding significantly to the price of the laptop, depending on the capacity, form factor and transfer speeds. , some manufacturers have begun shipping affordable, fast, energy-efficient drives priced at $350 to computer manufacturers. For low-end applications, a USB flash drive may be obtainable for anywhere from $10 to $100 or so, depending on capacity; alternatively, a
CompactFlashCompactFlash is a mass storage device format used in portable electronic devices. Most CompactFlash devices contain flash memory in a standardized enclosure. The format was first specified and produced by SanDisk in 1994...
card may be paired with a CF-to-IDE or CF-to-SATA converter at a similar cost. Either of these requires that write-cycle endurance issues be managed, either by refraining from storing frequently written files on the drive or by using a
flash file systemA flash file system is a file system designed for storing files on flash memory devices. These are becoming more prevalent as the number of mobile devices is increasing, the cost per memory size decreases, and the capacity of flash memories increases....
. Standard CompactFlash cards usually have write speeds of 7 to 15 MB/s while the more expensive upmarket cards claim speeds of up to 60 MB/s.
One of the first mainstream releases of SSD was the
XO LaptopThe XO-1, previously known as the $100 Laptop, Children's Machine, and 2B1, is an inexpensive subnotebook computer intended to be distributed to children in developing countries around the world, to provide them with access to knowledge, and opportunities to "explore, experiment and express...
, built as part of the One Laptop Per Child project. Mass production of these computers, built for children in developing countries, began in December 2007. These machines use 1,024 MiB SLC NAND flash as primary storage which is considered more suitable for the harsher than normal conditions in which they are expected to be used.
DellDell, Inc. is an American multinational information technology corporation based in 1 Dell Way, Round Rock, Texas, United States, that develops, sells and supports computers and related products and services. Bearing the name of its founder, Michael Dell, the company is one of the largest...
began shipping ultra-portable laptops with SanDisk SSDs on April 26, 2007.
AsusASUSTeK Computer Incorporated is a multinational computer technology and consumer electronics product manufacturer headquartered in Taipei, Taiwan. Its product range includes motherboards, desktops, laptops, monitors, tablet PCs, servers and mobile phones...
released the
Eee PCThe Asus Eee PC is a subnotebook/netbook computer line from ASUSTeK Computer Incorporated, and a part of the Asus Eee product family. At the time of its introduction in late 2007, it was noted for its combination of a light weight, Linux operating system, solid-state drive , and relatively low cost...
subnotebookA subnotebook is a class of laptop computers that are smaller and lighter than a typical laptop....
on October 16, 2007, and after a successful commercial start in 2007, it was expected to ship several million PCs in 2008, with 2, 4 or 8 gigabytes of flash memory. On January 31, 2008, Apple Inc. released the
MacBook AirThe MacBook Air family is a line of Apple ultraportable Macintosh notebook computers.The first-generation MacBook Air was a 13.3"-only model, previously promoted as the World's Thinnest Notebook, introduced at the Macworld Conference & Expo on January 15, 2008. It featured a custom Intel Merom CPU...
, a thin laptop with optional 64 GB SSD. The Apple Store cost was $999 more for this option, as compared to that of an 80 GB 4200 RPM hard disk drive. Another option, the Lenovo
ThinkPadThinkPad is line of laptop computers originally sold by IBM but now produced by Lenovo. They are known for their boxy black design, which was modeled after a traditional Japanese lunchbox...
X300 with a 64 gigabyte SSD, was announced by Lenovo in February 2008, and is, , available to consumers in some countries. On August 26, 2008, Lenovo released ThinkPad X301 with 128GB SSD option which adds approximately $200 US.
In 2008, low end netbooks appeared with SSDs. In 2009, SSDs began to appear in laptops.
On January 14, 2008,
EMCEMC Corporation , a Financial Times Global 500, Fortune 500 and S&P 500 company, develops, delivers and supports information infrastructure and virtual infrastructure hardware, software, and services. EMC is headquartered in Hopkinton, Massachusetts, USA.Former Intel executive Richard Egan and his...
became the first enterprise storage vendor to ship flash-based SSDs into its product portfolio.
In late 2008,
SunSun Microsystems, Inc. was a company that sold :computers, computer components, :computer software, and :information technology services. Sun was founded on February 24, 1982...
released the
Sun Storage 7000 Unified Storage Systems (codenamed Amber Road), which use both solid state drives and conventional hard drives to take advantage of the speed offered by SSDs and the economy and capacity offered by conventional hard disks.
DellDell, Inc. is an American multinational information technology corporation based in 1 Dell Way, Round Rock, Texas, United States, that develops, sells and supports computers and related products and services. Bearing the name of its founder, Michael Dell, the company is one of the largest...
began to offer optional 256 GB solid state drives on select notebook models in January 2009.
In May 2009, Toshiba launched a laptop with a 512 GB SSD.
, Apple's
MacBook AirThe MacBook Air family is a line of Apple ultraportable Macintosh notebook computers.The first-generation MacBook Air was a 13.3"-only model, previously promoted as the World's Thinnest Notebook, introduced at the Macworld Conference & Expo on January 15, 2008. It featured a custom Intel Merom CPU...
line carries solid state drives as standard.
In December 2010,
OCZOCZ Technology is a manufacturer of computer hardware based in San Jose, California, USA. Since entering the memory market in 2002, OCZ has targeted its products primarily at the computer hardware enthusiast market, first producing performance DDR RAM, Video Cards, USB drives, and various Cooling...
RevoDrive X2 PCIe SSD was available in 100GB to 960GB capacities delivering speeds over 740MB/s sequential speeds and random small file writes up to 120,000 IOPS.
In November 2010, Fusion-io released its highest performing SSD drive named ioDrive Octal utilising PCI-Express x16 Gen 2.0 interface with storage space of 5.12TB, read speed of 6.0GB/s, write speed of 4.4GB/s and a low latency of 30 microseconds. It has 1.19M Read 512 byte IOPS and 1.18M Write 512 byte IOPS.
Quality and performance
SSD technology is developing rapidly. Most of the performance measurements used on disk drives with rotating media are also used on SSDs. Performance of flash-based SSDs is difficult to benchmark because of the wide range of possible conditions. In a test performed in 2010 by Xssist, using
IOmeterIometer is an I/O subsystem measurement and characterization tool for single and clustered systems. It is used as a benchmark and troubleshooting tool and is easily configured to replicate the behaviour of many popular applications...
, 4 KB random 70% read/30% write, queue depth 4, the IOPS delivered by the Intel X25-E 64 GB G1 started around 10,000 IOPs, and dropped sharply after 8 minutes to 4,000 IOPS, and continued to decrease gradually for the next 42 minutes. IOPS vary between 3,000 to 4,000 from around 50 minutes onwards for the rest of the 8+ hours test run.
Write amplification is the major reason for the change in performance of an SSD over time. Enterprise grade drives try to avoid this performance variation by increasing over provisioning, and by employing wear-leveling algorithms that move data around only when the drives are not being heavily utilized.
Applications
Until 2009, SSDs were mainly used in those aspects of
mission criticalMission critical refers to any factor of a system whose failure will result in the failure of business operations. That is, it is critical to the organization's 'mission'....
applications where the speed of the storage system needed to be as fast as possible. Since flash memory has become a common component of SSDs, the falling prices and increased densities have made it more financially attractive for many other applications. Organizations that can benefit from faster access of system data include equity trading companies,
telecommunicationTelecommunication is the transmission of information over significant distances to communicate. In earlier times, telecommunications involved the use of visual signals, such as beacons, smoke signals, semaphore telegraphs, signal flags, and optical heliographs, or audio messages via coded...
corporations,
streaming mediaStreaming media is multimedia that is constantly received by and presented to an end-user while being delivered by a streaming provider.The term "presented" is used in this article in a general sense that includes audio or video playback. The name refers to the delivery method of the medium rather...
and
video editingThe term video editing can refer to:* Linear video editing, using video tape* Non-linear editing system , using computers with video editing software* Offline editing* Online editing...
firms. The list of applications which could benefit from faster storage is vast. Any company can assess the
ROIIn finance, rate of return , also known as return on investment , rate of profit or sometimes just return, is the ratio of money gained or lost on an investment relative to the amount of money invested. The amount of money gained or lost may be referred to as interest, profit/loss, gain/loss, or...
from adding SSDs to their own applications to best understand if that will be cost effective for them.
Flash-based solid-state drives can be used to create network appliances from general-purpose
personal computerA personal computer is any general-purpose computer whose size, capabilities, and original sales price make it useful for individuals, and which is intended to be operated directly by an end-user with no intervening computer operator...
hardware. A
write protectedWrite protection is any physical mechanism that prevents modification or erasure of valuable data on a device. Most commercial software, audio and video is sold pre-protected.-Examples:...
flash drive containing the operating system and application software can substitute for larger, less reliable disk drives or CD-ROMs. Appliances built this way can provide an inexpensive alternative to expensive router and firewall hardware.
SSDs based on an SD card with a live SD operating system are easily write-locked. Combined with a
cloud computingCloud computing is the delivery of computing as a service rather than a product, whereby shared resources, software, and information are provided to computers and other devices as a utility over a network ....
environment or other writable medium, to maintain
persistencePersistence in computer science refers to the characteristic of state that outlives the process that created it. Without this capability, state would only exist in RAM, and would be lost when this RAM loses power, such as a computer shutdown....
, an
OSAn operating system is a set of programs that manage computer hardware resources and provide common services for application software. The operating system is the most important type of system software in a computer system...
bootedIn computing, booting is a process that begins when a user turns on a computer system and prepares the computer to perform its normal operations. On modern computers, this typically involves loading and starting an operating system. The boot sequence is the initial set of operations that the...
from a write-locked SD card is robust, rugged, reliable, and impervious to permanent corruption. If the running OS degrades, simply turning the machine off and then on returns it back to its initial virgin uncorrupted state and thus is particularly solid. The SD card installed OS does not require removal of corrupted components since it was write-locked though any written media may need to be restored.
In 2011 Intel introduced a caching mechanism for their Z68 chipset (and mobile derivatives) called
Smart Response TechnologyIn computing, Smart Response Technology is a proprietary caching mechanism introduced in 2011 by Intel for their Z68 chipset , which allows a SATA solid-state drive to function as cache for a hard disk drive.SRT is implemented in the device driver and firmware...
, which allows a
SATASata is a traditional dish from the Malaysian state of Terengganu, consisting of spiced fish meat wrapped in banana leaves and cooked on a grill.It is a type of Malaysian fish cake, or otak-otak...
SSD to be used as a
cacheIn computer engineering, a cache is a component that transparently stores data so that future requests for that data can be served faster. The data that is stored within a cache might be values that have been computed earlier or duplicates of original values that are stored elsewhere...
(configurable as write-through or write-back) for a conventional, magnetic hard disk drive. A similar technology is available on
HighPointHighpoint can refer to:*Highpoint, Florida, an unincorporated community near Tampa Bay*Highpoint Center for Printmaking, a print workshop in Minneapolis*Highpoint Shopping Centre in Melbourne, Australia*Highpoint I, a set of apartment buildings in London...
's RocketHybrid PCIe card.
Hybrid driveA Hybrid Drive, Hybrid Hard Drive , or Hybrid Hard Disk Drive is a type of large-buffer computer hard disk drive. It is different from standard hard drives in that it integrates a cache using non-volatile memory or even a small solid-state drive...
s (H-HDSs) are based on the same principle, but integrate some amount of flash memory on board of a conventional drive instead of using a separate SSD. The flash layer in these drives can be accessed independently from the
magnetic storageMagnetic storage and magnetic recording are terms from engineering referring to the storage of data on a magnetized medium. Magnetic storage uses different patterns of magnetization in a magnetizable material to store data and is a form of non-volatile memory. The information is accessed using...
by the host using ATA-8 commands, allowing the operating system to manage it. For example Microsoft's ReadyDrive technology explicitly stores portions of the hibernation file in the cache of these drives when the system hibernates, making the subsequent resume faster.
SSD-optimized file systems
There are a number of computer
file systemA file system is a means to organize data expected to be retained after a program terminates by providing procedures to store, retrieve and update data, as well as manage the available space on the device which contain it. A file system organizes data in an efficient manner and is tuned to the...
s which are optimized for solid-state drives. Some of the more popular or notable are listed below.
Microsoft Windows
Versions of
WindowsMicrosoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
prior to Windows 7 are optimized for hard disk drives rather than SSDs.
Windows VistaWindows Vista is an operating system released in several variations developed by Microsoft for use on personal computers, including home and business desktops, laptops, tablet PCs, and media center PCs...
includes
ReadyBoostReadyBoost is a disk cache component of Microsoft Windows, first introduced with Microsoft's Windows Vista in 2006 and bundled with Windows 7 in 2009...
to exploit characteristics of USB-connected flash devices, but for SSDs it only improves the default partition alignment to prevent read-modify-write operations which reduce the speed of the SSD. This is because most SSDs are typically aligned on 4 KB sectors and most OSes are based on 512 byte sectors with the default partition set up unaligned . The proper alignment really does not help the SSD's endurance over the life of the drive, however some Vista operations, if not disabled, can shorten the life of the SSD. Disk
defragmentationIn the maintenance of file systems, defragmentation is a process that reduces the amount of fragmentation. It does this by physically organizing the contents of the mass storage device used to store files into the smallest number of contiguous regions . It also attempts to create larger regions of...
should be disabled because the location of the file components on an SSD doesn't significantly impact its performance, but moving the files to make them contiguous using the Windows Defrag routine will cause unnecessary write wear on the limited number of P/E cycles on the SSD. The Superfetch feature will not materially improve the performance of the system and causes additional overhead in the system and SSD, although it does not cause wear.
Windows 7 is optimized for SSDs as well as for traditional magnetic hard disks. The OS looks for the presence of an SSD and operates differently with that drive. If an SSD is present, Windows 7 will disable disk defragmentation, Superfetch, ReadyBoost, and other boot-time and application prefetching operations. It also includes support for the
TRIMIn computing, a TRIM command allows an operating system to inform a solid-state drive which blocks of data are no longer considered in use and can be wiped internally. While TRIM is frequently spelled in capital letters, it is not an acronym; it is merely a command name.TRIM was introduced soon...
command to reduce garbage collection of data which the OS has already determined is no longer valid. Without support for TRIM, the SSD would be unaware of this data being invalid and would unnecessarily continue to rewrite this data during garbage collection causing further wear on the SSD.
ZFS
Solaris as of version 10 Update 6 (released in October 2008), and recent versions of
OpenSolarisOpenSolaris was an open source computer operating system based on Solaris created by Sun Microsystems. It was also the name of the project initiated by Sun to build a developer and user community around the software...
and Solaris Express Community Edition can use SSDs as a performance booster for
ZFSIn computing, ZFS is a combined file system and logical volume manager designed by Sun Microsystems. The features of ZFS include data integrity verification against data corruption modes , support for high storage capacities, integration of the concepts of filesystem and volume management,...
. A low-latency SSD can be used for the ZFS Intent Log (ZIL), where it is named the SLOG. This is used every time a synchronous write to the disk occurs. An SSD (not necessarily with a low-latency) may also be used for the level 2
Adaptive Replacement CacheAdaptive Replacement Cache is a page replacement algorithm withbetter performance than LRU developed at the IBM Almaden Research Center. This is accomplished by keeping track of both Frequently Used and Recently Used pages plus a recent eviction history for both...
(L2ARC), which is used to cache data for reading. When used either alone or in combination, large increases in performance are generally seen.
FreeBSD
In addition to ZFS features described above,
UFSThe Unix file system is a file system used by many Unix and Unix-like operating systems. It is also called the Berkeley Fast File System, the BSD Fast File System or FFS...
supports the
TRIMIn computing, a TRIM command allows an operating system to inform a solid-state drive which blocks of data are no longer considered in use and can be wiped internally. While TRIM is frequently spelled in capital letters, it is not an acronym; it is merely a command name.TRIM was introduced soon...
command.
Linux systems
The Linux kernel supports the TRIM function starting with version 2.6.33. The
ext4The ext4 or fourth extended filesystem is a journaling file system for Linux, developed as the successor to ext3.It was born as a series of backward compatible extensions to ext3, many of them originally developed by Cluster File Systems for the Lustre file system between 2003 and 2006, meant to...
file system is supported when mounted using the "discard" parameter. The most recent disk utilities (and therefore installation software that make use of them) also apply proper partition alignment.
Mac OS X
Mac OS X 10.7 (Lion) supports TRIM, as does OS X 10.6.8 Snow Leopard. It is possible to add TRIM to versions earlier than 10.6.8.
Standardization organizations
The following are noted standardization organizations and bodies that work to create standards for solid-state drives (and other computer storage devices). It also includes organizations who promote the use of solid-state drives. This is not necessarily an exhaustive list.
| Organization or Committee |
Subcommittee of: |
Purpose |
| INCITS |
N/A |
Coordinates technical standards activity between ANSI in the USA and joint ISO/IEC committees worldwide |
| T10 |
INCITS |
SCSI Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it...
|
| T11 |
INCITS |
FCFibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards...
|
| T13 |
INCITS |
ATAParallel ATA , originally ATA, is an interface standard for the connection of storage devices such as hard disks, solid-state drives, floppy drives, and optical disc drives in computers. The standard is maintained by X3/INCITS committee...
|
| JEDEC The JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...
|
N/A |
Develops open standards and publications for the microelectronics industry |
| JC-64.8 The JEDEC Solid State Technology Association, formerly known as the Joint Electron Devices Engineering Council , is an independent semiconductor engineering trade organization and standardization body...
|
JEDEC |
Focuses on solid-state drive standards and publications |
| NVMHCI |
N/A |
Provides standard software and hardware programming interfaces for nonvolatile memory subsystems |
| SATA-IO Serial ATA International Organization is an independent, non-profit organization which provides the computing industry with guidance and support for implementing the SATA specification. SATA-IO was developed by and for leading industry companies...
|
N/A |
Provides the industry with guidance and support for implementing the SATA specification |
| SFF Committee The Small Form Factor committee is an ad hoc electronics industry group formed to quickly develop interoperability specifications ....
|
N/A |
Works on storage industry standards needing prompt attention when not addressed by other standards committees |
| SNIA An association of producers and consumers of storage networking products, whose goal is to further storage networking technology and applications.The Storage Networking Industry Association, or SNIA, was incorporated in December, 1997, and is a registered 501 non-profit trade association...
|
N/A |
Develops and promotes standards, technologies, and educational services in the management of information |
| SSSI |
SNIA |
Fosters the growth and success of solid state storage |