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Virtualization

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Title: Virtualization  
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Virtualization

Virtualization, in computing, refers to the act of creating a virtual (rather than actual) version of something, including but not limited to a virtual computer hardware platform, operating system (OS), storage device, or computer network resources.

Virtualization began in 1960s mainframe computers as a method of logically dividing the mainframes' resources for different applications. Since then, the meaning of the term has broadened.[1]

Contents

  • Hardware virtualization 1
    • Snapshots 1.1
    • Migration 1.2
    • Failover 1.3
    • Video game console emulation 1.4
    • Licensing 1.5
  • Desktop virtualization 2
  • Other types 3
  • Nested virtualization 4
  • See also 5
  • References 6

Hardware virtualization

Hardware virtualization or platform virtualization refers to the creation of a virtual machine that acts like a real computer with an operating system. Software executed on these virtual machines is separated from the underlying hardware resources. For example, a computer that is running Microsoft Windows may host a virtual machine that looks like a computer with the Ubuntu Linux operating system; Ubuntu-based software can be run on the virtual machine.[2][3]

In hardware virtualization, the host machine is the actual machine on which the virtualization takes place, and the guest machine is the virtual machine. The words host and guest are used to distinguish the software that runs on the physical machine from the software that runs on the virtual machine. The software or firmware that creates a virtual machine on the host hardware is called a hypervisor or Virtual Machine Manager.

Different types of hardware virtualization include:

  • Full virtualization – almost complete simulation of the actual hardware to allow software, which typically consists of a guest operating system, to run unmodified.
  • Partial virtualization – some but not all of the target environment is simulated. Some guest programs, therefore, may need modifications to run in this virtual environment.
  • Paravirtualization – a hardware environment is not simulated; however, the guest programs are executed in their own isolated domains, as if they are running on a separate system. Guest programs need to be specifically modified to run in this environment.

Hardware-assisted virtualization is a way of improving overall efficiency of virtualization. It involves CPUs that provide support for virtualization in hardware, and other hardware components that help improve the performance of a guest environment.

Hardware virtualization can be viewed as part of an overall trend in enterprise IT that includes

Hardware virtualization is not the same as hardware emulation. In hardware emulation, a piece of hardware imitates another, while in hardware virtualization, a hypervisor (a piece of software) imitates a particular piece of computer hardware or the entire computer. Furthermore, a hypervisor is not the same as an emulator; both are computer programs that imitate hardware, but their domain of use in language differs.

Snapshots

A snapshot is the state of a virtual machine, and generally its storage devices, at an exact point in time. A snapshot enables the virtual machine's state at the time of the snapshot to be restored later, effectively undoing any changes that occurred afterwards. This capability is useful as a backup technique, for example, prior to performing a risky operation.

Virtual machines frequently use virtual disks for their storage; in a very simple example, a 10-gigabyte hard disk drive is simulated with a 10-gigabyte flat file. Any requests by the VM for a location on its physical disk are transparently translated into an operation on the corresponding file. Once such a translation layer is present, however, it is possible to intercept the operations and send them to different files, depending on various criteria. Every time a snapshot is taken, a new file is created, and used as an overlay for its predecessors. New data are written to the topmost overlay; reading existing data, however, needs the overlay hierarchy to be scanned, resulting in accessing the most recent version. Thus, the entire stack of snapshots is virtually a single coherent disk; in that sense, creating snapshots works similarly to the incremental backup technique.

Other components of a virtual machine can also be included in a snapshot, such as the contents of its random-access memory (RAM), BIOS settings, or its configuration settings. "Save state" feature in video game console emulators is an example of such snapshots.

Restoring a snapshot consists of discarding or disregarding all overlay layers that are added after that snapshot, and directing all new changes to a new overlay.

Migration

The snapshots described above can be moved to another host machine with its own hypervisor; when the VM is temporarily stopped, snapshotted, moved, and then resumed on the new host, this is known as migration. If the older snapshots are kept in sync regularly, this operation can be quite fast, and allow the VM to provide uninterrupted service while its prior physical host is, for example, taken down for physical maintenance.

Failover

Similar to teleportation above, failover allows the VM to continue operations if the host fails. However, in this case, the VM continues operation from the last-known coherent state, rather than the current state, based on whatever materials the backup server was last provided with.

Video game console emulation

A video game console emulator is a program that allows a personal computer or video game console to emulate a different video game console's behavior. Video game console emulators and hypervisors both perform hardware virtualization; words like "virtualization", "virtual machine", "host" and "guest" are not used in conjunction with console emulators.

Licensing

Virtual machines running proprietary operating systems require licensing, regardless of the host machine's operating system. For example, installing Microsoft Windows into a VM guest requires its licensing requirements to be satisfied.

Desktop virtualization

Desktop virtualization is the concept of separating the logical desktop from the physical machine.

One form of desktop virtualization, virtual desktop infrastructure (VDI), can be thought of as a more advanced form of hardware virtualization. Rather than interacting with a host computer directly via a keyboard, mouse, and monitor, the user interacts with the host computer using another desktop computer or a mobile device by means of a network connection, such as a LAN, Wireless LAN or even the Internet. In addition, the host computer in this scenario becomes a server computer capable of hosting multiple virtual machines at the same time for multiple users.[4]

As organizations continue to virtualize and converge their data center environment, client architectures also continue to evolve in order to take advantage of the predictability, continuity, and quality of service delivered by their converged infrastructure. For example, companies like HP and IBM provide a hybrid VDI model with a range of virtualization software and delivery models to improve upon the limitations of distributed client computing.[5] Selected client environments move workloads from PCs and other devices to data center servers, creating well-managed virtual clients, with applications and client operating environments hosted on servers and storage in the data center. For users, this means they can access their desktop from any location, without being tied to a single client device. Since the resources are centralized, users moving between work locations can still access the same client environment with their applications and data.[5] For IT administrators, this means a more centralized, efficient client environment that is easier to maintain and able to more quickly respond to the changing needs of the user and business.[6][7]

Another form, session virtualization, allows multiple users to connect and log into a shared but powerful computer over the network and use it simultaneously. Each is given a desktop and a personal folder in which they store their files.[4] With multiseat configuration, session virtualization can be accomplished using a single PC with multiple monitors keyboards and mice connected.

  1. ^ Graziano, Charles. "A performance analysis of Xen and KVM hypervisors for hosting the Xen Worlds Project". Retrieved 2013-01-29. 
  2. ^ Turban, E; King, D; Lee, J; Viehland, D (2008). "Chapter 19: Building E-Commerce Applications and Infrastructure". Electronic Commerce A Managerial Perspective. Prentice-Hall. p. 27. 
  3. ^ "Virtualization in education".  
  4. ^ a b "Strategies for Embracing Consumerization". Microsoft Corporation. April 2011. p. 9. Retrieved 22 July 2011. 
  5. ^ a b Chernicoff, David, “HP VDI Moves to Center Stage,” ZDNet, August 19, 2011.
  6. ^ Baburajan, Rajani, "The Rising Cloud Storage Market Opportunity Strengthens Vendors," infoTECH, August 24, 2011. It.tmcnet.com. 2011-08-24.
  7. ^ Oestreich, Ken, "Converged Infrastructure," CTO Forum, November 15, 2010. Thectoforum.com.
  8. ^ "Desktop Virtualization Tries to Find Its Place in the Enterprise". Dell.com. Retrieved 2012-06-19. 
  9. ^ "HVD: the cloud's silver lining". Intrinsic Technology. Retrieved 30 August 2012. 
  10. ^ "Enterprise Systems Group White paper, Page 5". Enterprise Strategy Group White Paper written and published on August 20, 2011 by Mark Peters. 
  11. ^ Orit Wasserman,  

References

See also

Nested virtualization refers to simulation of a virtual machine within another. The general concept can be extended to an arbitrary depth. A nested guest virtual machine need not be homogenous with its host virtual machine (e.g., application virtualization within hardware virtualization).[11]

Nested virtualization

Network
  • Data virtualization, the presentation of data as an abstract layer, independent of underlying database systems, structures and storage.
  • Database virtualization, the decoupling of the database layer, which lies between the storage and application layers within the application stack over all.
Data
Storage
Memory
Software

Other types

Moving virtualised desktops into the cloud creates hosted virtual desktops (HVD), where the desktop images are centrally managed and maintained by a specialist hosting firm. Benefits include scalability and the reduction of capital expenditure, which is replaced by a monthly operational cost.[9]

Desktop virtualization simplifies software versioning and patch management, where the new image is simply updated on the server, and the desktop gets the updated version when it reboots. It also enables centralized control over what applications the user is allowed to have access to on the workstation. [8]

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