Desktop virtualization
Encyclopedia
Desktop virtualization as a concept
, separates a personal computer
desktop environment
from a physical machine using the client–server model of computing.
Virtual desktop infrastructure, sometimes referred to as virtual desktop interface (VDI) is the server computing model
enabling desktop virtualization, encompassing the hardware and software systems required to support the virtualized environment.
Many enterprise-level implementations of this technology store the resulting "virtualized" desktop on a remote central server, instead of on the local storage of a remote client; thus, when users work from their local machine, all of the programs, applications, processes, and data used are kept on the server and run centrally. This allows users to run operating system and execute applications from a smartphone
or thin client
which exceed the user hardware's ability to run.
Some virtualization platforms allow the user to simultaneously run multiple virtual machines on local hardware, such as a laptop, using hypervisor
technology. Virtual machine images are created and maintained on a central server, and changes to the desktop VMs are propagated to all user machines through the network, thus combining both the advantages of portability afforded by local hypervisor execution and of central image management. This approach requires more capable user hardware capable of running the local VM images, such as a personal computer
or notebook computer, and thus is not as portable as the pure client-server model.
This latter model can also be implemented without the server component, allowing smaller organizations and individuals to take advantage of the flexibility of multiple desktop VMs on a single hardware platform without additional network and server resources.
The desktop virtualization model allows the use of virtual machines to let multiple network subscribers maintain individualized desktops on a single, centrally located computer or server. The central machine may operate at a residence, business, or data center. Users may be geographically scattered, but all must be connected to the central machine by a local area network
, a wide area network
, or the public Internet.
Microsoft
included a technology called virtual desktop infrastructure in Windows Server 2008.
Intel has built hardware virtualization support into its processors, citing a growing need for client-hosted virtualization.
—where the controlling computer will work almost the same as on a duplicate desktop, except that the actions of the controlling computer may be almost unnoticeable on the remote computer display. This differs from simple remote desktop software
in that several people can use the same controlling computer at once, without disturbing each others' work. This could be useful for several administrators doing different tasks on the same server. It can also be used for using hardware attached to the controlled computer, without disturbing a person who may already be using the computer.
However, a major use spreads the resources of one machine to several users. In some cases one can buy one large computer (or server) and several thin client
s or dumb terminals, rather than purchasing a complete computer for each physical workstation
. The controlling thin-client computers need only enough resources to run the remote controlling software, therefore virtualization can provide a very simple and cheap computing system. Users of such a "thin client" or "dumb terminal" may not even know that "their" software actually runs on another computer. If one already has enough computers, but they are not powerful enough, only one new computer may be needed, with the old ones re-usable as thin clients
of user information because all data can be maintained and backed-up in the data center.
Potential advantages include:
Limitations of desktop virtualization include:
Both Hosted and Centralized modes rely upon a constant network or internet connection to the server where the VDI instance is running. This model is similar in concept to thin clients, in that the client device only displays the virtual desktop. For this reason, a constant network connection is required.
The Remote Synchronization model allows users to copy a VDI instance to a system, and then run the virtual desktop without a connection. In this model, users normally use virtual machines that are running on a centralized server, but can copy an image to be used locally when traveling. This dis-connected or untethered mode of operation has its own set of advantages and disadvantages compared to traditional desktops and centralized VDI desktops.
The Client-hosted model only uses centralized servers to manage virtual machine images, always running virtual machines on laptops or desktops. Local execution eliminates the infrastructure required for VDI execution servers in the data center and also reduces network bandwidth consumption since the virtual machines are executing locally and not over a remote network.
. Hosted virtual desktop services generally include a managed desktop client operating-system
configuration. Security may be physical, through a local storage-area network, or virtual through data-center policies. Transferring information technology infrastructure to an outsourced model can shift accounting for the associated costs from capital expenses
to operating expense
s.
According to a report by Gartner
, hosted services accounted for more than 500,000 desktop units as of March 2009, but will grow to 49 million desktop units by 2013, and may make up as much as 40% of the worldwide "professional PC market" by revenue.
For this model, there are two modes for VDI, static (also called persistent) and dynamic (also called non-persistent).
In static mode, there is a one-to-one mapping of a desktop to a user. That is, each user gets a unique desktop, and the desktop image must be managed and maintained.
In a dynamic mode, there is often a master image of the desktop stored, all user data is stored separately from the desktop. When a user logs in and requests a desktop, a VM that is “cloned” from the master image is combined with his personal data and applications.
An image is copied to a local system, where it may run without requiring a network connection. Images are "checked out" for a period of time, and typically need to be refreshed periodically. The local system typically runs an operating system, along with a hypervisor, which in turn runs the VDI instance. Thus, this model requires more local CPU, memory and disk space than alternative forms of VDI. Additionally, security and other issues can be of greater concern for this model. However, this model enables traveling and other highly mobile users to utilize virtual desktops without network connectivity restraints.
Because this model is designed for local execution as the primary mode of operation, it usually builds in additional security capabilities such as full disk encryption, time-based lockout, and remote kill capabilities. Some solutions have been optimized to use a type-1 client hypervisor
, which eliminates the need for an additional operating system on the client, thereby reducing system requirements and increasing performance and security.
Memory (RAM) requirements is another item that is typically straightforward to calculate utilizing vendor supplied sizing information. A common amount of RAM required for a virtual desktop instance is 1 or 2 GB of physical memory, although this varies based on workload, applications, operating system and other factors.
Client-hosted virtualization does not require VDI execution servers, because the virtual machines are executed on end-point machines.
Incremental network investments typically are not required for client-hosted VDI, because the network load is similar to the network consumption for traditional PC management operations.
Storage can play a significant role in the overall performance of VDI. There are several storage technologies which can have a significant beneficial impact on VDI performance. Client-hosted VDI typically reduces storage requirements by an order of magnitude because storage is only used for offline backups.
Concept
The word concept is used in ordinary language as well as in almost all academic disciplines. Particularly in philosophy, psychology and cognitive sciences the term is much used and much discussed. WordNet defines concept: "conception, construct ". However, the meaning of the term concept is much...
, separates a 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...
desktop environment
Desktop environment
In graphical computing, a desktop environment commonly refers to a style of graphical user interface derived from the desktop metaphor that is seen on most modern personal computers. These GUIs help the user in easily accessing, configuring, and modifying many important and frequently accessed...
from a physical machine using the client–server model of computing.
Virtual desktop infrastructure, sometimes referred to as virtual desktop interface (VDI) is the server computing model
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"...
enabling desktop virtualization, encompassing the hardware and software systems required to support the virtualized environment.
Many enterprise-level implementations of this technology store the resulting "virtualized" desktop on a remote central server, instead of on the local storage of a remote client; thus, when users work from their local machine, all of the programs, applications, processes, and data used are kept on the server and run centrally. This allows users to run operating system and execute applications from a smartphone
Smartphone
A smartphone is a high-end mobile phone built on a mobile computing platform, with more advanced computing ability and connectivity than a contemporary feature phone. The first smartphones were devices that mainly combined the functions of a personal digital assistant and a mobile phone or camera...
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...
which exceed the user hardware's ability to run.
Some virtualization platforms allow the user to simultaneously run multiple virtual machines on local hardware, such as a laptop, using hypervisor
Hypervisor
In computing, a hypervisor, also called virtual machine manager , is one of many hardware virtualization techniques that allow multiple operating systems, termed guests, to run concurrently on a host computer. It is so named because it is conceptually one level higher than a supervisory program...
technology. Virtual machine images are created and maintained on a central server, and changes to the desktop VMs are propagated to all user machines through the network, thus combining both the advantages of portability afforded by local hypervisor execution and of central image management. This approach requires more capable user hardware capable of running the local VM images, such as a 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...
or notebook computer, and thus is not as portable as the pure client-server model.
This latter model can also be implemented without the server component, allowing smaller organizations and individuals to take advantage of the flexibility of multiple desktop VMs on a single hardware platform without additional network and server resources.
Technical definition
Desktop virtualization involves encapsulating and delivering either access to an entire information system environment or the environment itself to a remote client device. The client device may use an entirely different hardware architecture from that used by the projected desktop environment, and may also be based upon an entirely different operating system.The desktop virtualization model allows the use of virtual machines to let multiple network subscribers maintain individualized desktops on a single, centrally located computer or server. The central machine may operate at a residence, business, or data center. Users may be geographically scattered, but all must be connected to the central machine by a local area network
Local area network
A local area network is a computer network that interconnects computers in a limited area such as a home, school, computer laboratory, or office building...
, a wide area network
Wide area network
A wide area network is a telecommunication network that covers a broad area . Business and government entities utilize WANs to relay data among employees, clients, buyers, and suppliers from various geographical locations...
, or the public Internet.
VDI
Virtual desktop infrastructure (VDI) is the practice of hosting a desktop operating system within a virtual machine (VM) running on a hosted, centralized or remote server. The term was coined by VMware Inc.Microsoft
Microsoft
Microsoft 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...
included a technology called virtual desktop infrastructure in Windows Server 2008.
Intel has built hardware virtualization support into its processors, citing a growing need for client-hosted virtualization.
Uses
A simple use for desktop virtualization involves remote administrationRemote administration
Remote administration refers to any method of controlling a computer from a remote location.Software that allows remote administration is becoming increasingly common and is often used when it is difficult or impractical to be physically near a system in order to use it, or in order to access web...
—where the controlling computer will work almost the same as on a duplicate desktop, except that the actions of the controlling computer may be almost unnoticeable on the remote computer display. This differs from simple remote desktop software
Remote desktop software
In computing, the term remote desktop refers to a software or an OS feature allowing applications, either command line programs or graphical applications, to be run remotely on a server, while being displayed locally. Remote desktop applications have varying features...
in that several people can use the same controlling computer at once, without disturbing each others' work. This could be useful for several administrators doing different tasks on the same server. It can also be used for using hardware attached to the controlled computer, without disturbing a person who may already be using the computer.
However, a major use spreads the resources of one machine to several users. In some cases one can buy one large computer (or server) and several 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 or dumb terminals, rather than purchasing a complete computer for each physical workstation
Desk
A desk is a furniture form and a class of table often used in a work or office setting for reading or writing on or using a computer. Desks often have one or more drawers to store office supplies and papers. Unlike a regular table, usually only one side of a desk is suitable to sit on . Not all...
. The controlling thin-client computers need only enough resources to run the remote controlling software, therefore virtualization can provide a very simple and cheap computing system. Users of such a "thin client" or "dumb terminal" may not even know that "their" software actually runs on another computer. If one already has enough computers, but they are not powerful enough, only one new computer may be needed, with the old ones re-usable as thin clients
Advantages and disadvantages
The shared resources model inherent in desktop virtualization offers advantages over the traditional model, in which every computer operates as a completely self-contained unit with its own operating system, peripherals, and application programs. Overall hardware expenses may diminish as users can share resources allocated to them on an as-needed basis. Virtualization potentially improves the data integrityData integrity
Data Integrity in its broadest meaning refers to the trustworthiness of system resources over their entire life cycle. In more analytic terms, it is "the representational faithfulness of information to the true state of the object that the information represents, where representational faithfulness...
of user information because all data can be maintained and backed-up in the data center.
Potential advantages include:
- simpler provisioningProvisioningIn telecommunication, provisioning is the process of preparing and equipping a network to allow it to provide services to its users. In NS/EP telecommunications services, "provisioning" equates to "initiation" and includes altering the state of an existing priority service or capability.In a...
of new desktops - reduced downtimeDowntimeThe term downtime is used to refer to periods when a system is unavailable.Downtime or outage duration refers to a period of time that a system fails to provide or perform its primary function...
in the event of server or client hardware-failures - lower cost of deploying new applications
- desktop image-management capabilities
- longer refresh cycle for client desktop infrastructure
- secure remote access to an enterprise desktop environment
Limitations of desktop virtualization include:
- potential security risks if the network is not properly managed
- challenges in setting up and maintaining drivers for printers and other peripherals
- difficulty in running certain complex applications (such as 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...
) - increased downtimeDowntimeThe term downtime is used to refer to periods when a system is unavailable.Downtime or outage duration refers to a period of time that a system fails to provide or perform its primary function...
in the event of network failures, which can be prevented by the use of a clustered file system - reliance on connectivity to corporate or public network
- complexity and high costs of VDI deployment and management
VDI Modes of Operation
There are essentially four models for VDI operation.- Hosted (delivered as a service)
- Centralized
- Remote Synchronization
- Client-Hosted
Both Hosted and Centralized modes rely upon a constant network or internet connection to the server where the VDI instance is running. This model is similar in concept to thin clients, in that the client device only displays the virtual desktop. For this reason, a constant network connection is required.
The Remote Synchronization model allows users to copy a VDI instance to a system, and then run the virtual desktop without a connection. In this model, users normally use virtual machines that are running on a centralized server, but can copy an image to be used locally when traveling. This dis-connected or untethered mode of operation has its own set of advantages and disadvantages compared to traditional desktops and centralized VDI desktops.
The Client-hosted model only uses centralized servers to manage virtual machine images, always running virtual machines on laptops or desktops. Local execution eliminates the infrastructure required for VDI execution servers in the data center and also reduces network bandwidth consumption since the virtual machines are executing locally and not over a remote network.
Hosted virtual desktops
Hosted virtual desktops result from desktop virtualization services provided through an outsourced, hosted subscription modelSoftware as a Service
Software as a service , sometimes referred to as "on-demand software," is a software delivery model in which software and its associated data are hosted centrally and are typically accessed by users using a thin client, normally using a web browser over the Internet.SaaS has become a common...
. Hosted virtual desktop services generally include a managed desktop client 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...
configuration. Security may be physical, through a local storage-area network, or virtual through data-center policies. Transferring information technology infrastructure to an outsourced model can shift accounting for the associated costs from capital expenses
Capital expenditure
Capital expenditures are expenditures creating future benefits. A capital expenditure is incurred when a business spends money either to buy fixed assets or to add to the value of an existing fixed asset with a useful life extending beyond the taxable year...
to operating expense
Operating expense
An operating expense, operating expenditure, operational expense, operational expenditure or OPEX is an ongoing cost for running a product, business, or system . Its counterpart, a capital expenditure , is the cost of developing or providing non-consumable parts for the product or system...
s.
According to a report by Gartner
Gartner
Gartner, Inc. is an information technology research and advisory firm headquartered in Stamford, Connecticut, United States. It was known as GartnerGroup until 2001....
, hosted services accounted for more than 500,000 desktop units as of March 2009, but will grow to 49 million desktop units by 2013, and may make up as much as 40% of the worldwide "professional PC market" by revenue.
Centralized virtual desktops
With this model, all VDI instances are hosted on one or more centralized servers. Data is maintained on storage systems attached to the centralized servers.For this model, there are two modes for VDI, static (also called persistent) and dynamic (also called non-persistent).
In static mode, there is a one-to-one mapping of a desktop to a user. That is, each user gets a unique desktop, and the desktop image must be managed and maintained.
In a dynamic mode, there is often a master image of the desktop stored, all user data is stored separately from the desktop. When a user logs in and requests a desktop, a VM that is “cloned” from the master image is combined with his personal data and applications.
Remote Synchronized virtual desktops
Remote VDI instances takes the concept of a centralized VDI image that is maintained by an IT department, and adds the ability to work while disconnected from a central server or internet.An image is copied to a local system, where it may run without requiring a network connection. Images are "checked out" for a period of time, and typically need to be refreshed periodically. The local system typically runs an operating system, along with a hypervisor, which in turn runs the VDI instance. Thus, this model requires more local CPU, memory and disk space than alternative forms of VDI. Additionally, security and other issues can be of greater concern for this model. However, this model enables traveling and other highly mobile users to utilize virtual desktops without network connectivity restraints.
Client-hosted Virtual Desktops
Client-hosted VDI uses centralized image management but runs the desktop locally on a client hypervisor on a conventional desktop or laptop. Some client-hosted virtualization solutions also offer options for centrally storing the data on a SAN, which still executes locally on a desktop PC – taking advantage of local CPU and graphics processing capabilities.Because this model is designed for local execution as the primary mode of operation, it usually builds in additional security capabilities such as full disk encryption, time-based lockout, and remote kill capabilities. Some solutions have been optimized to use a type-1 client hypervisor
Hypervisor
In computing, a hypervisor, also called virtual machine manager , is one of many hardware virtualization techniques that allow multiple operating systems, termed guests, to run concurrently on a host computer. It is so named because it is conceptually one level higher than a supervisory program...
, which eliminates the need for an additional operating system on the client, thereby reducing system requirements and increasing performance and security.
IT Requirements for VDI
One of the primary concerns for companies implementing desktop virtualization, or VDI projects is understanding the Information Technology requirements. Virtualization software vendors typically provide sizing guidelines and reference architectures, along with total cost of ownership calculators and other tools to help decide what the cost implications will be for deploying virtual desktop infrastructure. The needs for infrastructure vary widely depending on whether a server-hosted or client-hosted approach.VDI Server Requirements
The system CPU and memory requirements may be calculated using a specific vendor's reference architecture or sizing guideline. Typically it is possible to over provision the CPU resources, thereby allocating 20 or 30 virtual desktop instances for a system with only 8 or 16 cores.Memory (RAM) requirements is another item that is typically straightforward to calculate utilizing vendor supplied sizing information. A common amount of RAM required for a virtual desktop instance is 1 or 2 GB of physical memory, although this varies based on workload, applications, operating system and other factors.
Client-hosted virtualization does not require VDI execution servers, because the virtual machines are executed on end-point machines.
VDI Network Requirements
The networking requirements, both between servers and clients running VDI images, along with internal server to server networks and storage networks are all considerations which also must be configured properly. Networking requirements can vary significantly, depending primarily upon the size of the server used to host the VDI sessions. For very large systems it is common to utilize multiple 1 Gb/s Ethernet LAN connections, with additional multiple 8 Gb/s FC SAN storage connections.Incremental network investments typically are not required for client-hosted VDI, because the network load is similar to the network consumption for traditional PC management operations.
VDI Storage Requirements
The impact of VDI on storage can be significant. Additionally, it can be difficult to understand the performance impact that a VDI deployment will have on storage systems. The primary focus of deployment guidelines regarding storage are how to calculate storage capacity requirements.Storage can play a significant role in the overall performance of VDI. There are several storage technologies which can have a significant beneficial impact on VDI performance. Client-hosted VDI typically reduces storage requirements by an order of magnitude because storage is only used for offline backups.
See also
- Dynamic desktopDynamic desktopDynamic desktop is a Windows-based workspace virtual desktop service, which is aware of the situation or context in which the user is operating at any given time; and dynamically adjusts the content and appearance of the workspace accordingly...
- Remote desktop softwareRemote desktop softwareIn computing, the term remote desktop refers to a software or an OS feature allowing applications, either command line programs or graphical applications, to be run remotely on a server, while being displayed locally. Remote desktop applications have varying features...
- Virtual machineVirtual machineA virtual machine is a "completely isolated guest operating system installation within a normal host operating system". Modern virtual machines are implemented with either software emulation or hardware virtualization or both together.-VM Definitions:A virtual machine is a software...
- Comparison of remote desktop software
- Application virtualizationApplication VirtualizationApplication virtualization is an umbrella term that describes software technologies that improve portability, manageability and compatibility of applications by encapsulating them from the underlying operating system on which they are executed. A fully virtualized application is not installed in...
- Workspace virtualizationWorkspace virtualizationWorkspace virtualization is a way of distributing applications to client computers using application virtualization however it also bundles several applications together into one complete workspace. It is an approach that encapsulates and isolates an entire computing workspace...
- Multiseat desktop virtualizationMultiseat desktop virtualizationMultiSeat Desktop Virtualization is a method by which a common desktop PC, with extra keyboards, mice, and video screens directly attached to it, can be used to install, load, and concurrently run multiple operating systems. These operating systems can be the same across all "seats" or they can be...
- User environment managementUser environment managementUser environment management is a computing term used to describe the management of a user's experience within their desktop environment.-The user environment:...