Diskless workstation
Encyclopedia
A diskless node is a workstation
or personal computer
without disk drives, which employs network booting
to load its operating system
from a server
. (A computer may also be said to act as a diskless node, if its disks are unused and network booting is used.)
Diskless nodes (or computers acting as such) are sometimes known as network computer
s or hybrid clients. Hybrid client may either just mean diskless node, or it may be used in a more particular sense to mean a diskless node which runs some, but not all, applications
remotely, as in the thin client
computing architecture.
Advantages of diskless nodes can include lower production cost, lower running costs, quieter operation, and manageability advantages (for example, centrally managed software installation).
In many universities and in some large organizations, PC
s are used in a similar configuration, with some or all applications stored remotely but executed
locally—again, for manageability reasons. However, these are not diskless nodes if they still boot
from a local hard drive.
, thus using their own CPU and RAM
to run software
, but do not store data persistently—that task is handed off to a server. This is distinct from thin client
s, in which all significant processing happens remotely, on the server—the only software that runs on a thin client is the "thin" (i.e. relatively small and simple) client software, which handles simple input/output tasks to communicate with the user, such as drawing a dialog box
on the display
or waiting for user input.
A collective term encompassing both thin client computing, and its technological predecessor, text terminals (which are text-only), is centralized computing
. Thin client
s and text terminals can both require powerful central processing facilities in the servers, in order to perform all significant processing tasks for all of the clients.
Diskless nodes can be seen as a compromise between fat client
s (such as ordinary personal computer
s) and centralized computing, using central storage for efficiency, but not requiring centralized processing, and making efficient use of the powerful processing power of even the slowest of contemporary CPUs
, which would tend to sit idle for much of the time under the centralized computing model.
. In some cases, removable storage may be used to initiate the bootstrap process, such as a USB flash drive
, or other bootable media such as a floppy disk
, CD or DVD. However, the firmware
in many modern computers can be configured to locate a server and begin the bootup process automatically, without the need to insert bootable media.
For network auto-booting, the Preboot Execution Environment
(PXE) or Bootstrap Protocol (BOOTP) network protocols are commonly used to find a server with files for booting the device. Standard full-size desktop PCs are able to be network-booted in this manner with an add-on network card that includes a UNDI
boot ROM. Diskless network booting is commonly a built-in feature of desktop and laptop PCs intended for business use, since it can be used on an otherwise disk-booted standard desktop computer to remotely run diagnostics, to install software, or to apply a disk image
to the local hard drive.
After the bootstrapping process has been initiated, as described above, bootstrapping will take place according to one of three main approaches.
NT Servers and even DEC Pathworks
servers.
Third party software Vendors such as Qualystem (acquired by Neoware
), LanWorks (acquired by 3Com
), Ardence (acquired by Citrix),APCT and Xtreamining Technology have developed and marketed software products aimed to remote-boot newer versions of the Windows
product line: Windows 95 OSR2 and Windows 98 were supported by Qualystem and Lanworks, Windows NT was supported by APCT and Ardence (called VenturCom at that time), and Windows 2000/XP/2003/Vista/Windows 7 are supported by Hewlett Packard (which acquired Neoware
which had previously acquired Qualystem) and Citrix Systems
(which acquired Ardence
).
configurations among the nodes), installing software and maintaining installed software can be more efficient. Furthermore, any system changes made during operation (due to user action, worms, viruses, etc.) can be either wiped out when the power is removed (if the image is copied to a local RAM disk) such as Windows XP Embedded remote boot or prohibited entirely (if the image is a network filesystem). This allows use in public access areas (such as libraries) or in schools etc. where users might wish to experiment or attempt to "hack" the system.
However, it is not necessary to implement network booting to achieve either of the above advantages - ordinary PCs
(with the help of appropriate software) can be configured to download and reinstall their operating systems on (e.g.) a nightly basis, with extra work compared to using shared disk image that diskless nodes boot off.
Modern diskless nodes can share the very same disk image, using a 1:N relationship (1 disk image used simultaneously by N diskless nodes). This makes it very easy to install and maintain software applications: The administrator needs to install or maintain the application only once, and the clients can get the new application as soon as they boot off the updated image. Disk image sharing is made possible because they use the write cache: No client competes for any writing in a shared disk image, because each client writes to its own cache.
All the modern diskless nodes systems can also use a 1:1 Client-to-DiskImage relationship, where one client "owns" one disk image and writes directly into said disk image. No write cache is used then.
Making a modification in a shared disk image is usually made this way:
1. The administrator makes a copy of the shared disk image that he/she wants to update (this can be done easily because the disk image file is opened only for reading)
2. The administrator boots a diskless node in 1:1 mode (unshared mode) from the copy of the disk image he/she just made
3. The administrator makes any modification to the disk image (for instance install a new software application, apply patches or hotfixes...)
4. The administrator shutdowns the diskless node that was using the disk image in 1:1 mode
5. The administrator shares the modified disk image
6. The diskless nodes use the shared disk image (1:N) as soon as they are rebooted.
s which support redundant operation, and storage area network
s which allow hot-adding of storage without any interruption. Further, it means that losses of disk drives to mechanical or electrical failure—which are statistically highly probable events over a timeframe of years, with a large number of disks involved—are often both less likely to happen (because there are typically less disk drives that can fail) and less likely to cause interruption (because they would likely be part of RAID arrays). This also means that the nodes themselves are less likely to have hardware failures than fat client
s.
Diskless nodes share these advantages with thin client
s.
Large numbers of nodes making demands on the same server simultaneously can slow down everyone's experience. However, this can be mitigated by installing large amounts of RAM
on the server (which speeds up read operations by improving caching
performance), by adding more servers (which distributes the I/O workload), or by adding more disks to a RAID array (which distributes the physical I/O workload). In any case this is also a problem which can affect any client-server network to some extent, since, of course, fat clients also use servers to store user data.
Indeed, user data may be much more significant in size and may be accessed far more frequently than operating systems and programs in some environments, so moving to a diskless model will not necessarily cause a noticeable degradation in performance.
Greater network bandwidth (i.e. capacity) will also be used in a diskless model, compared to a fat client model. This does not necessarily mean that a higher capacity network infrastructure will need to be installed—it could simply mean that a higher proportion of the existing network capacity will be used.
Finally, the combination of network data transfer latencies
(physically transferring the data over the network) and contention latencies (waiting for the server to process other node's requests before yours) can lead to an unacceptable degradation in performance compared to using local drives, depending on the nature of the application and the capacity of the network infrastructure and the server.
Diskless machines may also consume little power and make little noise, which implies potential environmental benefits
and makes them ideal for some computer cluster applications.
s (using Microsoft Windows Terminal Server
or other such software), since much lower specification hardware can be used for the client (which essentially acts as a simple "window" into the central server which is actually running the users operating system as a login session
). Of course, diskless nodes can also be used as thin clients. Moreover, thin client computers are increasing in power to the point where they are becoming suitable as fully-fledged diskless workstations for some applications.
Both thin client and diskless node architectures employ diskless clients which have advantages over fat clients (see above), but differ with regard to the location of processing.
Workstation
A workstation is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems...
or personal computer
Personal computer
A 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...
without disk drives, which employs network booting
Network booting
Network booting is the process of booting a computer from a network rather than a local drive. This method of booting can be used by routers, diskless workstations and centrally managed computers such as public computers at libraries and schools...
to load its operating system
Operating system
An 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...
from a server
Server (computing)
In 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"...
. (A computer may also be said to act as a diskless node, if its disks are unused and network booting is used.)
Diskless nodes (or computers acting as such) are sometimes known as network computer
Network computer
Network Computer is a trademark of Oracle Corporation that was used, from approximately 1996 to 2000, to market a range of diskless desktop computer devices. The devices were designed and manufactured by an alliance, which included Sun Microsystems, IBM, and others...
s or hybrid clients. Hybrid client may either just mean diskless node, or it may be used in a more particular sense to mean a diskless node which runs some, but not all, applications
Application software
Application software, also known as an application or an "app", is computer software designed to help the user to perform specific tasks. Examples include enterprise software, accounting software, office suites, graphics software and media players. Many application programs deal principally with...
remotely, as in the thin client
Thin client
A thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself...
computing architecture.
Advantages of diskless nodes can include lower production cost, lower running costs, quieter operation, and manageability advantages (for example, centrally managed software installation).
In many universities and in some large organizations, PC
Personal computer
A 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...
s are used in a similar configuration, with some or all applications stored remotely but executed
Execution (computers)
Execution in computer and software engineering is the process by which a computer or a virtual machine carries out the instructions of a computer program. The instructions in the program trigger sequences of simple actions on the executing machine...
locally—again, for manageability reasons. However, these are not diskless nodes if they still 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...
from a local hard drive.
Distinction between diskless nodes and centralized computing
Diskless nodes process dataData (computing)
In computer science, data is information in a form suitable for use with a computer. Data is often distinguished from programs. A program is a sequence of instructions that detail a task for the computer to perform...
, thus using their own CPU and 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...
to run software
Computer software
Computer software, or just software, is a collection of computer programs and related data that provide the instructions for telling a computer what to do and how to do it....
, but do not store data persistently—that task is handed off to a server. This is distinct from thin client
Thin client
A thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself...
s, in which all significant processing happens remotely, on the server—the only software that runs on a thin client is the "thin" (i.e. relatively small and simple) client software, which handles simple input/output tasks to communicate with the user, such as drawing a dialog box
Dialog box
In a graphical user interface of computers, a dialog box is a type of window used to enable reciprocal communication or "dialog" between a computer and its user. It may communicate information to the user, prompt the user for a response, or both...
on the display
Display device
A display device is an output device for presentation of information in visual or tactile form...
or waiting for user input.
A collective term encompassing both thin client computing, and its technological predecessor, text terminals (which are text-only), is centralized computing
Centralized computing
Centralized computing is computing done at a central location, using terminals that are attached to a central computer. The computer itself may control all the peripherals directly , or they may be attached via a terminal server...
. Thin client
Thin client
A thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself...
s and text terminals can both require powerful central processing facilities in the servers, in order to perform all significant processing tasks for all of the clients.
Diskless nodes can be seen as a compromise between fat client
Fat client
A fat client is a computer in client–server architecture or networks that typically provides rich functionality independent of the central server...
s (such as ordinary personal computer
Personal computer
A 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...
s) and centralized computing, using central storage for efficiency, but not requiring centralized processing, and making efficient use of the powerful processing power of even the slowest of contemporary CPUs
Central processing unit
The central processing unit is the portion of a computer system that carries out the instructions of a computer program, to perform the basic arithmetical, logical, and input/output operations of the system. The CPU plays a role somewhat analogous to the brain in the computer. The term has been in...
, which would tend to sit idle for much of the time under the centralized computing model.
| Centralized computing Centralized computing Centralized computing is computing done at a central location, using terminals that are attached to a central computer. The computer itself may control all the peripherals directly , or they may be attached via a terminal server... or Thin client Thin client A thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself... |
Diskless node | Fat client Fat client A fat client is a computer in client–server architecture or networks that typically provides rich functionality independent of the central server... |
|
|---|---|---|---|
| Local hard drives used | |||
| Local general-purpose processing used |
Principles of operation
The operating system (OS) for a diskless node is loaded from a server, using network bootingNetwork booting
Network booting is the process of booting a computer from a network rather than a local drive. This method of booting can be used by routers, diskless workstations and centrally managed computers such as public computers at libraries and schools...
. In some cases, removable storage may be used to initiate the bootstrap process, such as a USB flash drive
USB flash drive
A flash drive is a data storage device that consists of flash memory with an integrated Universal Serial Bus interface. flash drives are typically removable and rewritable, and physically much smaller than a floppy disk. Most weigh less than 30 g...
, or other bootable media such as a floppy disk
Floppy disk
A 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...
, CD or DVD. However, the firmware
Firmware
In electronic systems and computing, firmware is a term often used to denote the fixed, usually rather small, programs and/or data structures that internally control various electronic devices...
in many modern computers can be configured to locate a server and begin the bootup process automatically, without the need to insert bootable media.
For network auto-booting, the Preboot Execution Environment
Preboot Execution Environment
The Preboot eXecution Environment is an environment to boot computers using a network interface independently of data storage devices or installed operating systems.PXE was introduced as part of the Wired for Management framework by Intel and is described in the specification The Preboot...
(PXE) or Bootstrap Protocol (BOOTP) network protocols are commonly used to find a server with files for booting the device. Standard full-size desktop PCs are able to be network-booted in this manner with an add-on network card that includes a UNDI
Undi
Undi is a village and a mandal in West Godavari district in the state of Andhra Pradesh in India. It is located about 39 kilometers from Eluru town.-Geography:Undi is located at...
boot ROM. Diskless network booting is commonly a built-in feature of desktop and laptop PCs intended for business use, since it can be used on an otherwise disk-booted standard desktop computer to remotely run diagnostics, to install software, or to apply a disk image
Disk image
A disk image is a single file or storage device containing the complete contents and structure representing a data storage medium or device, such as a hard drive, tape drive, floppy disk, CD/DVD/BD, or USB flash drive, although an image of an optical disc may be referred to as an optical disc image...
to the local hard drive.
After the bootstrapping process has been initiated, as described above, bootstrapping will take place according to one of three main approaches.
- In the first approach (used, for example, by the Linux Terminal Server ProjectLinux Terminal Server ProjectLinux Terminal Server Project is a free and open source terminal server for Linux that allows many people to simultaneously use the same computer. Applications run on the server with a terminal known as a thin client handling input and output...
), the kernel is loaded into memory and then the rest of the operating system is accessed via a network filesystem connection to the server. (A small RAM diskRAM 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...
may be created to store temporary files locally.) This approach is sometimes called the "NFS root" technique when used with Linux or Unix client operating systems.
- In the second approach, the kernel of the OS is loaded, and part of the system's memory is configured as a large RAM disk, and then the remainder of the OS image is fetched and loaded into the RAM disk. This is the implementation that MicrosoftMicrosoftMicrosoft Corporation is an American public multinational corporation headquartered in Redmond, Washington, USA that develops, manufactures, licenses, and supports a wide range of products and services predominantly related to computing through its various product divisions...
has chosen for its Windows XP embedded remote boot feature.
- In the third approach, disk operations are virtualized and are actually translated into a network protocol. The data that are usually stored in a disk drive are then stored in virtual disks files homed on a server. The disk operations such as requests to read/write disk sectors are translated into corresponding network requests and processed by a service or daemon running on the server side. This is the implementation that is used by NeowareNeowareNeoware was a company that manufactured and marketed a type of computer hardware called thin clients.It also developed and marketed enterprise software, thin client appliances, and related services aimed at reducing the TCO of IT infrastructure....
Image Manager, Ardence, VHD and various "boot over iSCSI" products. This third approach differs from the first approach because what is remote is not a file systemFile 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...
but actually a disk device (or raw deviceRaw deviceIn computing, specifically Unix-like operating systems, a raw device is a special kind of block device file that allows accessing a storage device such as a hard drive directly, bypassing the operating system's caches and buffers...
) and that the client OS is not aware that it is not running off a hard disk. This is why this approach is sometimes named "Virtual Hard Disk" or "Network Virtual Disk".
Diskless Windows nodes
Windows 3.x and Windows 95 OSR1 supported Remote Boot operations, from Netware servers, WindowsMicrosoft Windows
Microsoft 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...
NT Servers and even DEC Pathworks
Pathworks
Pathworks was the tradename used by Digital Equipment Corporation of Maynard, Massachusetts for a series of programs that eased the interoperation of Digital's minicomputers with personal computers....
servers.
Third party software Vendors such as Qualystem (acquired by Neoware
Neoware
Neoware was a company that manufactured and marketed a type of computer hardware called thin clients.It also developed and marketed enterprise software, thin client appliances, and related services aimed at reducing the TCO of IT infrastructure....
), LanWorks (acquired by 3Com
3Com
3Com was a pioneering digital electronics manufacturer best known for its computer network infrastructure products. The company was co-founded in 1979 by Robert Metcalfe, Howard Charney, Bruce Borden, and Greg Shaw...
), Ardence (acquired by Citrix),APCT and Xtreamining Technology have developed and marketed software products aimed to remote-boot newer versions of the Windows
Microsoft Windows
Microsoft 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...
product line: Windows 95 OSR2 and Windows 98 were supported by Qualystem and Lanworks, Windows NT was supported by APCT and Ardence (called VenturCom at that time), and Windows 2000/XP/2003/Vista/Windows 7 are supported by Hewlett Packard (which acquired Neoware
Neoware
Neoware was a company that manufactured and marketed a type of computer hardware called thin clients.It also developed and marketed enterprise software, thin client appliances, and related services aimed at reducing the TCO of IT infrastructure....
which had previously acquired Qualystem) and Citrix Systems
Citrix Systems
Citrix Systems, Inc. is a multinational corporation founded in 1989, that provides server and desktop virtualization, networking, software-as-a-service , and cloud computing technologies, including Xen open source products....
(which acquired Ardence
Ardence
Ardence, a Citrix Company, is a technology company headquartered in Waltham, Massachusetts with representatives in Washington, D.C.; Virginia Beach, VA; Chicago, IL; Denton, TX; and Europe, Middle East, Africa and India....
).
Software installation and maintenance
With essentially a single OS image for an array of machines (with perhaps some customizations for differences in hardwareHardware
Hardware is a general term for equipment such as keys, locks, hinges, latches, handles, wire, chains, plumbing supplies, tools, utensils, cutlery and machine parts. Household hardware is typically sold in hardware stores....
configurations among the nodes), installing software and maintaining installed software can be more efficient. Furthermore, any system changes made during operation (due to user action, worms, viruses, etc.) can be either wiped out when the power is removed (if the image is copied to a local RAM disk) such as Windows XP Embedded remote boot or prohibited entirely (if the image is a network filesystem). This allows use in public access areas (such as libraries) or in schools etc. where users might wish to experiment or attempt to "hack" the system.
However, it is not necessary to implement network booting to achieve either of the above advantages - ordinary PCs
Personal computer
A 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...
(with the help of appropriate software) can be configured to download and reinstall their operating systems on (e.g.) a nightly basis, with extra work compared to using shared disk image that diskless nodes boot off.
Modern diskless nodes can share the very same disk image, using a 1:N relationship (1 disk image used simultaneously by N diskless nodes). This makes it very easy to install and maintain software applications: The administrator needs to install or maintain the application only once, and the clients can get the new application as soon as they boot off the updated image. Disk image sharing is made possible because they use the write cache: No client competes for any writing in a shared disk image, because each client writes to its own cache.
All the modern diskless nodes systems can also use a 1:1 Client-to-DiskImage relationship, where one client "owns" one disk image and writes directly into said disk image. No write cache is used then.
Making a modification in a shared disk image is usually made this way:
1. The administrator makes a copy of the shared disk image that he/she wants to update (this can be done easily because the disk image file is opened only for reading)
2. The administrator boots a diskless node in 1:1 mode (unshared mode) from the copy of the disk image he/she just made
3. The administrator makes any modification to the disk image (for instance install a new software application, apply patches or hotfixes...)
4. The administrator shutdowns the diskless node that was using the disk image in 1:1 mode
5. The administrator shares the modified disk image
6. The diskless nodes use the shared disk image (1:N) as soon as they are rebooted.
Centralized storage
The use of central disk storage also makes more efficient use of disk storage. This can cut storage costs, freeing up capital to invest in more reliable, modern storage technologies, such as RAID arrayRAID
RAID is a storage technology that combines multiple disk drive components into a logical unit...
s which support redundant operation, and storage area network
Storage area network
A storage area network is a dedicated network that provides access to consolidated, block level data storage. SANs are primarily used to make storage devices, such as disk arrays, tape libraries, and optical jukeboxes, accessible to servers so that the devices appear like locally attached devices...
s which allow hot-adding of storage without any interruption. Further, it means that losses of disk drives to mechanical or electrical failure—which are statistically highly probable events over a timeframe of years, with a large number of disks involved—are often both less likely to happen (because there are typically less disk drives that can fail) and less likely to cause interruption (because they would likely be part of RAID arrays). This also means that the nodes themselves are less likely to have hardware failures than fat client
Fat client
A fat client is a computer in client–server architecture or networks that typically provides rich functionality independent of the central server...
s.
Diskless nodes share these advantages with thin client
Thin client
A thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself...
s.
Performance of centralized storage
However, this storage efficiency can come at a price. As often happens in computing, increased storage efficiency sometimes comes at the price of decreased performance.Large numbers of nodes making demands on the same server simultaneously can slow down everyone's experience. However, this can be mitigated by installing large amounts of 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...
on the server (which speeds up read operations by improving caching
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...
performance), by adding more servers (which distributes the I/O workload), or by adding more disks to a RAID array (which distributes the physical I/O workload). In any case this is also a problem which can affect any client-server network to some extent, since, of course, fat clients also use servers to store user data.
Indeed, user data may be much more significant in size and may be accessed far more frequently than operating systems and programs in some environments, so moving to a diskless model will not necessarily cause a noticeable degradation in performance.
Greater network bandwidth (i.e. capacity) will also be used in a diskless model, compared to a fat client model. This does not necessarily mean that a higher capacity network infrastructure will need to be installed—it could simply mean that a higher proportion of the existing network capacity will be used.
Finally, the combination of network data transfer latencies
Latency (engineering)
Latency 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:...
(physically transferring the data over the network) and contention latencies (waiting for the server to process other node's requests before yours) can lead to an unacceptable degradation in performance compared to using local drives, depending on the nature of the application and the capacity of the network infrastructure and the server.
Other advantages
Another example of a situation where a diskless node would be useful is in a possibly hazardous environment where computers are likely to be damaged or destroyed, thus making the need for inexpensive nodes, and minimal hardware a benefit. Again, thin clients can also be used here.Diskless machines may also consume little power and make little noise, which implies potential environmental benefits
Environmentally friendly
Environmentally friendly are terms used to refer to goods and services, laws, guidelines and policies claimed to inflict minimal or no harm on the environment....
and makes them ideal for some computer cluster applications.
Comparison with thin clients
Major corporations tend to instead implement thin clientThin client
A thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself...
s (using Microsoft Windows Terminal Server
Windows Server System
Microsoft Servers is a brand that encompasses a line of Microsoft server products. This includes the server editions of Microsoft Windows operating system itself, as well as products targeted at the wider business market...
or other such software), since much lower specification hardware can be used for the client (which essentially acts as a simple "window" into the central server which is actually running the users operating system as a login session
Login session
In computing, a login session is the period of activity between a user logging in and logging out of a system.On Unix and Unix-like operating systems, a login session takes one of two main forms:...
). Of course, diskless nodes can also be used as thin clients. Moreover, thin client computers are increasing in power to the point where they are becoming suitable as fully-fledged diskless workstations for some applications.
Both thin client and diskless node architectures employ diskless clients which have advantages over fat clients (see above), but differ with regard to the location of processing.
Advantages of diskless nodes over thin clients
- Distributed load The processing load of diskless nodes is distributed. Each user gets its own processing isolated environment, barely affecting other users in the network, as long as their workload is not filesystem-intensive. Thin clients rely on the central server for the processing and thus require a fast server. When the central server is busy and slow, both kinds of clients will be affected, but thin clients will be slowed down completely, whereas diskless nodes will only be slowed down when accessing data on the server.
- Better multimedia performance. Diskless nodes have advantages over thin clients in multimediaMultimediaMultimedia is media and content that uses a combination of different content forms. The term can be used as a noun or as an adjective describing a medium as having multiple content forms. The term is used in contrast to media which use only rudimentary computer display such as text-only, or...
-rich applications that would be bandwidth intensive if fully served. For example, diskless nodes are well suited for video gaming. - Peripheral support Diskless nodes are typically ordinary personal computerPersonal 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...
s or workstationWorkstationA workstation is a high-end microcomputer designed for technical or scientific applications. Intended primarily to be used by one person at a time, they are commonly connected to a local area network and run multi-user operating systems...
s with no hard drives supplied, which means the usual large variety of peripheralPeripheralA peripheral is a device attached to a host computer, but not part of it, and is more or less dependent on the host. It expands the host's capabilities, but does not form part of the core computer architecture....
s can be added. By contrast, thin clients are typically very small, sealed boxes with no possibility for internal expansion, and limited or non-existent possibility for external expansion. Even if e.g. a USB device can be physically attached to a thin client, the thin client software might not support peripherals beyond the basic input and output devices - for example, it may not be compatible with graphics tabletGraphics tabletA graphics tablet is a computer input device that enables a user to hand-draw images and graphics, similar to the way a person draws images with a pencil and paper. These tablets may also be used to capture data or handwritten signatures...
s, digital cameraDigital cameraA digital camera is a camera that takes video or still photographs, or both, digitally by recording images via an electronic image sensor. It is the main device used in the field of digital photography...
s or scannerImage scannerIn computing, an image scanner—often abbreviated to just scanner—is a device that optically scans images, printed text, handwriting, or an object, and converts it to a digital image. Common examples found in offices are variations of the desktop scanner where the document is placed on a glass...
s.
Advantages of thin clients over diskless nodes
- The hardware is cheaper on thin clients, since processing requirements on the client are minimal, and 3D acceleration and elaborate audio support are not usually provided. Of course, a diskless node can also be purchased with a cheap CPU and minimal multimedia support, if suitable. Thus, cost savings may be smaller than they first appear for some organizations. However, many large organizations habitually buy hardware with a higher than necessary specification to meet the needs of particular applications and uses, or to ensure future proofing (see below). There are also less "rational" reasons for overspecifying hardware which quite often come into play: departments wastefully using up budgets in order to retain their current budget levels for next year; and uncertainty about the future, or lack of technical knowledge, or lack of care and attention, when choosing PC specifications. Taking all these factors into account, thin clients may bring the most substantial savings, as only the servers are likely to be substantially "gold-plated" and/or "future-proofed" in the thin client model.
- Future proofing is not much of an issue for thin clients, which are likely to remain useful for the entirety of their replacement cycle - one to four years, or even longer - as the burden is on the servers. There are issues when it comes to diskless nodes, as the processing load is potentially much higher, thus meaning more consideration is required when purchasing. Thin client networks may require significantly more powerful servers in the future, whereas a diskless nodes network may in future need a server upgrade, a client upgrade, or both.
- Thin client networks have less network bandwidth consumption potentially, since much data is simply read by the server and processed there, and only transferred to the client in small pieces, as and when needed for display. Also, transferring graphical data to the display is usually more suited for efficient data compressionData compressionIn computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....
and optimisation technologies (see e.g. NX technologyNX technologyNX technology is a computer program that handles remote X Window System connections, and attempts to greatly improve on the performance of the native X display protocol to the point that it can be usable over a slow link such as a dial-up modem...
) than transferring arbitrary programsComputer programA computer program is a sequence of instructions written to perform a specified task with a computer. A computer requires programs to function, typically executing the program's instructions in a central processor. The program has an executable form that the computer can use directly to execute...
, or user data. In many typical application scenarios, both total bandwidth consumption and "burst" consumption would be expected to be less for an efficient thin client, than for a diskless node.
See also
- Thin clientThin clientA thin client is a computer or a computer program which depends heavily on some other computer to fulfill its traditional computational roles. This stands in contrast to the traditional fat client, a computer designed to take on these roles by itself...
- Network block deviceNetwork block deviceIn Linux, a network block device is a device node whose content is provided by a remote machine. Typically, network block devices are used to access a storage device that does not physically reside in the local machine but on a remote one...
- Diskless Remote Boot in Linux
- Preboot Execution EnvironmentPreboot Execution EnvironmentThe Preboot eXecution Environment is an environment to boot computers using a network interface independently of data storage devices or installed operating systems.PXE was introduced as part of the Wired for Management framework by Intel and is described in the specification The Preboot...
External links
- http://www.faqs.org/docs/Linux-HOWTO/Diskless-HOWTO.html
- Network Block Device home page http://nbd.sourceforge.net/
- Wyse WSM http://www.wyse.com/products/software/wsm/index.asp