Hybrid drive

Hybrid drive

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A Hybrid Drive, Hybrid Hard Drive (HHD), or Hybrid Hard Disk Drive (H-HDD) is a type of large-buffer computer hard disk drive. It is different from standard hard drives in that it integrates a cache
Cache
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...

 using non-volatile memory or even a small solid-state drive
Solid-state drive
A solid-state drive , sometimes called a solid-state disk or electronic disk, is a data storage device that uses solid-state memory to store persistent data with the intention of providing access in the same manner of a traditional block i/o hard disk drive...

 (SSD). Although the cache typically uses non-volatile
Non-volatile memory
Non-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...

 flash memory
Flash memory
Flash 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...

, some drives use battery-backed volatile
Volatile memory
Volatile 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...

 RAM
Ram
-Animals:*Ram, an uncastrated male sheep*Ram cichlid, a species of freshwater fish endemic to Colombia and Venezuela-Military:*Battering ram*Ramming, a military tactic in which one vehicle runs into another...

 (a hybrid RAM disk). The flash memory buffer can speed up repeated reads to the same location; a RAM buffer speeds both reads and writes, but must be written to backup storage before power is lost.

History


In 2007 Seagate
Seagate Technology
Seagate Technology is one of the world's largest manufacturers of hard disk drives. Incorporated in 1978 as Shugart Technology, Seagate is currently incorporated in Dublin, Ireland and has its principal executive offices in Scotts Valley, California, United States.-1970s:On November 1, 1979...

 and Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...

 both introduced hybrid HDDs primarily targeted to OEMs
Original Equipment Manufacturer
An original equipment manufacturer, or OEM, manufactures products or components that are purchased by a company and retailed under that purchasing company's brand name. OEM refers to the company that originally manufactured the product. When referring to automotive parts, OEM designates a...

 notebook computer manufacturers. Although the technology was initially supported by Microsoft, a number of issues prevented their success over the next year in the market with Windows Vista
Windows Vista
Windows 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...

.

In May 2010, Seagate launched the Momentus XT 7200RPM 2.5" solid state hybrid drive which has a 4GB SLC NAND chip, which is used as a read-only cache managed by the drive itself. Seagate calls this Adaptive Memory and claims it removes the OS, driver, and software dependency previously required to take advantage of the integrated Flash memory. The SSD portion of this new drive is also now a larger 4 GB, compared to 256 MB in the past. Benchmark results conducted and published by Seagate of the Momentus XT place the 7200 RPM hybrid drive's performance firmly between high-end 10,000 RPM drives and solid-state drive
Solid-state drive
A solid-state drive , sometimes called a solid-state disk or electronic disk, is a data storage device that uses solid-state memory to store persistent data with the intention of providing access in the same manner of a traditional block i/o hard disk drive...

s on a number of tasks, such as system boot time and application launch speed. For example, according to these benchmarks, system boot time using this hybrid drive is approximately 41% faster than the same task using a non-hybrid 7200 RPM drive, while a "best-in-class" solid-state drive performs approximately 44% faster than a standard 7200 RPM drive on the same test. According to The Register
The Register
The Register is a British technology news and opinion website. It was founded by John Lettice, Mike Magee and Ross Alderson in 1994 as a newsletter called "Chip Connection", initially as an email service...

, in the first year after launch Seagate sold 350,000 units of this hybrid drive.

In 2011, Hitachi
Hitachi
Hitachi is a multinational corporation specializing in high-technology.Hitachi may also refer to:*Hitachi, Ibaraki, Japan*Hitachi province, former province of Japan*Prince Hitachi and Princess Hitachi, members of the Japanese imperial family...

 LG (HLDS) will introduce its own hybrid hardwares.

Operation


Unlike most standard hard drives, the hybrid drive in its normal state has its platters at rest, with the motor not consuming power or generating heat. Any data written to the hybrid drive is written to the buffer; there is no risk of data loss in the event of power failure as the buffer's flash memory
Flash memory
Flash 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...

 is not volatile. When reading data from the platters extra data is read and stored in buffer memory (which need not be non-volatile flash memory) in the hope of anticipating future requirements as in any disk cache
Disk buffer
In computer storage, disk buffer is the embedded memory in a hard drive acting as a buffer between the rest of the computer and the physical hard disk platter that is used for storage...

. Data required for the next boot-up can be stored in the non-volatile buffer before shutting down the computer.

The hybrid drive's platters will spin up to move data from the write buffer to the platters when nearly full, and to read data which is not in the cache.

Early estimates place the actual hard drive usage (when the platters are spinning) at anywhere between 1.25% and 10% for typical single users, although there are obviously situations where platter usage will be much higher, such as the encoding or editing of very large video files, producing reports from a database, etc.

As of early 2008 the special features of hybrid drives are only taken advantage of by Microsoft's Windows Vista and Windows 7 operating systems. The files required for booting are stored in the fast flash memory, reducing boot time by about 11%. Microsoft uses the name ReadyDrive to describe the software side of this technology. While hybrid drives are not required for Vista Premium certification of laptops, some confusion arose as to whether such drives would be mandatory.

The hybrid drive command interface will be standardized in the new revision 8 of the ATA
AT Attachment
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...

 standard. The ATA-8 draft provides a new set of commands allowing the host to manage the on-board flash memory or other types of non-volatile (NV) cache, for example pinning some LBAs
Logical block addressing
Logical block addressing is a common scheme used for specifying the location of blocks of data stored on computer storage devices, generally secondary storage systems such as hard disks....

 in the NV cache.

In 2010 Seagate released the Momentus XT, which uses so-called "adaptive memory" for its SSD portion, which is not reliant on driver support from the operating system. This removes the need for a special operating system, and the speed benefits can be used by any OS.

Claimed benefits


Manufacturers claim several benefits of the hybrid drive over standard hard drives, especially for use in notebook computers
Laptop
A laptop, also called a notebook, is a personal computer for mobile use. A laptop integrates most of the typical components of a desktop computer, including a display, a keyboard, a pointing device and speakers into a single unit...

. Samsung claims the chief benefits are speed of data access and consequent faster computer boot
Booting
In 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...

 process, decreased power consumption, and improved reliability.

Claimed drawbacks


There are some inherent drawbacks to the use of hybrid drives:
  • Lower performance (access time
    Access time
    Access time is the time delay or latency between a request to an electronic system, and the access being completed or the requested data returned....

    ) for non-cached data. If the data being accessed is not in the cache and the drive has spun down, access time will be greatly increased since the platters will need to spin-up
    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...

    .

  • Lower performance for small disk writes. Flash memory is significantly slower for writing small data, an effect that is amplified by use of journaling file system
    Journaling file system
    A journaling file system is a file system that keeps track of the changes that will be made in a journal before committing them to the main file system...

    s.

  • Slightly Increased cost. Hybrid hard drives are currently slightly more expensive than their non-hybrid counterparts, because of the higher cost of flash memory.

  • Reduced lifetime. A hard drive, once spinning, suffers almost no wear. A significant proportion of wear arises during the spin-up and spin-down processes. Indeed, the number of spin-ups is often given as the indication of the lifetime of a hard drive. Also, flash memory allows far fewer write cycles than a hard disk.

  • Increased perceived noise production. A hybrid hard drive, spinning up and down, may make drive noise more noticeable, especially with varying usage conditions (i.e., fans and hard drive spinning up on usage).

  • Increased power usage with spin-ups. A hybrid drive requires spin-up and spin-down more often than a normal hard drive, which is often spinning constantly. Hard drives also draw more power during spin-up.

  • Lower recoverability. Hybrid hard drives, based on storage to both a flash component and a hard drive component, and bound to use by a specific OS (i.e., Windows Vista), cannot be recovered after failure using classic hard drive recovery services.

Software implementation


Windows Vista and Windows 7 natively support the use of hybrid drives (ReadyDrive).

Hybrid drives may also be implemented in software, using other memory instead of a buffer built into the hard drive. Examples of such systems include the SuperCache caching software (implements hybrid RAM drive), and Windows ReadyBoost
ReadyBoost
ReadyBoost is a disk cache component of Microsoft Windows, first introduced with Microsoft's Windows Vista in 2006 and bundled with Windows 7 in 2009...

, which uses separate flash memory and hard disk to make a hybrid drive. Performance of the combined drive may be affected by the speed of the CPU and speed of the separate memory used, in addition to the speed of the hard drive interface.

The primary benefits of a hybrid drive may be created from a separate HDD and Flash memory device, managed by software, such as ReadyBoost
ReadyBoost
ReadyBoost is a disk cache component of Microsoft Windows, first introduced with Microsoft's Windows Vista in 2006 and bundled with Windows 7 in 2009...

 in Windows. A similar technology has been implemented by Diskeeper Corporation
Diskeeper Corporation
Diskeeper Corporation is the name of a software company based in Burbank, California, founded in 1981. The company's current name is derived from its flagship product, Diskeeper, a file system defragmentation software package for Microsoft Windows and VAX...

's ExpressCache software in Samsung
Samsung
The Samsung Group is a South Korean multinational conglomerate corporation headquartered in Samsung Town, Seoul, South Korea...

 laptops.

Hybrid RAM Disk


The hybrid RAM disk uses a large buffer of volatile SDRAM
SDRAM
Synchronous dynamic random access memory is dynamic random access memory that is synchronized with the system bus. Classic DRAM has an asynchronous interface, which means that it responds as quickly as possible to changes in control inputs...

 memory with battery backup instead of flash memory to cache hard disk data during normal use. The buffer reduces time and energy spent accessing the hard disk. If the RAM cache needs to be filled at startup, hybrid RAM disks may not speed the start-up process as much as flash based hybrid disks.

Battery backup allows data to be written to permanent storage when the device is shut down, and may allow data retention in RAM for limited periods.

Frequently accessed data is stored in DRAM, while all the data is stored in hard disk. As a result, the hard disk only needs to be accessed when the processor requests data that is not frequently used.

Hybrid RAM disks are claimed to offer significantly faster read-write speeds compared to standard hard disks.

Some RAM based SSDs may be used in combination with a hard disk to create a hybrid RAM disk.

When data is written to memory, the corresponding block in memory is marked as dirty, and all dirty blocks can be flushed to the actual hard drive based on the following criteria:
Time (e.g., every 10 seconds, flush all dirty data);
Threshold (when the ratio of dirty data to SSD size exceeds some predetermined value, flush the dirty data);
Loss of power/computer shutdown.

See also

  • Disk drive
  • Solid-state drive
    Solid-state drive
    A solid-state drive , sometimes called a solid-state disk or electronic disk, is a data storage device that uses solid-state memory to store persistent data with the intention of providing access in the same manner of a traditional block i/o hard disk drive...

  • Intel Turbo Memory
  • Smart Response Technology
    Smart Response Technology
    In 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...

     (Intel SSD Caching)
  • ReadyDrive
  • Non-volatile memory
    Non-volatile memory
    Non-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...


External links


Hybrid RAM disk