Hardware virtualization
Encyclopedia
Computer hardware virtualization is the virtualization
of computer
s or operating system
s. It hides the physical characteristics of a computing platform from users, instead showing another abstract computing platform. At its origins, the software that controled virtualization was called a "control program", but nowadays the terms "hypervisor
" or "virtual machine monitor" are preferred.
(sometimes called "pseudo machine"), a term which itself dates from the experimental IBM M44/44X
system. The creation and management of virtual machines has been called "platform virtualization", or "server virtualization", more recently.
Platform virtualization is performed on a given hardware platform by host software (a control program), which creates a simulated computer environment, a virtual machine (VM), for its guest software. The guest software is not limited to user applications; many hosts allow the execution of complete operating systems. The guest software executes as if it were running directly on the physical hardware, with several notable caveats. Access to physical system resources (such as the network access, display, keyboard, and disk storage) is generally managed at a more restrictive level than the host processor and system-memory. Guests are often restricted from accessing specific peripheral devices, or may be limited to a subset of the device's native capabilities, depending on the hardware access policy implemented by the virtualization host.
Virtualization often exacts performance penalties, both in resources required to run the hypervisor, and as well as in reduced performance on the virtual machine compared to running native on the physical machine.
However, when multiple VMs are concurrently running on the same physical host, each VM may exhibit a varying and unstable performance, which highly depends on the workload imposed on the system by other VMs, unless proper techniques are used for temporal isolation among virtual machines
.
There are several approaches to platform virtualization.
Examples of virtualization scenarios:
Running one or more applications that are not supported by the host OS : A virtual machine running the required guest OS could allow the desired applications to be run, without altering the host OS.
Evaluating an alternate operating system : The new OS could be run within a VM, without altering the host OS.
Server virtualization : Multiple virtual servers could be run on a single physical server, in order to more fully utilize the hardware resources of the physical server.
Duplicating specific environments : A virtual machine could, depending on the virtualization software used, be duplicated and installed on multiple hosts, or restored to a previously backed-up system state.
Creating a protected environment: if a guest OS running on a VM becomes damaged in a way that is difficult to repair, such as may occur when studying malware
or installing badly-behaved software, the VM may simply be discarded without harm to the host system, and a clean copy used next time.
) to be run in isolation. This approach was pioneered in 1966 with the IBM CP-40 and CP-67
, predecessors of the VM
family. Examples outside the mainframe field include Parallels Workstation
, Parallels Desktop for Mac
, VirtualBox
, Virtual Iron
, Oracle VM
, Virtual PC
, Virtual Server
, Hyper-V
, VMware Workstation
, VMware Server
(formerly GSX Server), KVM
, QEMU
, Adeos
, Mac-on-Linux
, Win4BSD, Win4Lin Pro
, and Egenera
vBlade technology.
) added similar features in their UltraSPARC T-Series processors in 2005. Examples of virtualization platforms adapted to such hardware include Linux KVM
, VMware Workstation
, VMware Fusion
, Microsoft Hyper-V, Microsoft Virtual PC
, Xen
, Parallels Desktop for Mac
, Oracle VM Server for SPARC
, VirtualBox
and Parallels Workstation
.
Hardware platforms with integrated virtualization technologies include:
In 2006 first-generation 32- and 64-bit x86 hardware support was found rarely to offer performance advantages over software virtualization.
s. Usually, this means that entire operating systems cannot run in the virtual machine – which would be the sign of full virtualization
– but that many applications can run. A key form of partial virtualization is address space virtualization, in which each virtual machine consists of an independent address space
. This capability requires address relocation
hardware, and has been present in most practical examples of partial virtualization.
Partial virtualization was an important historical milestone on the way to full virtualization. It was used in the first-generation time-sharing system CTSS, in the IBM M44/44X
experimental paging system, and arguably systems like MVS
and the Commodore 64
(a couple of 'task switch' programs). The term could also be used to describe any operating system that provides separate address spaces for individual users or processes, including many that today would not be considered virtual machine
systems. Experience with partial virtualization, and its limitations, led to the creation of the first full virtualization system (IBM's CP-40
, the first iteration of CP/CMS
which would eventually become IBM's VM family
). (Many more recent systems, such as Microsoft Windows
and Linux
, as well as the remaining categories below, also use this basic approach.)
Partial virtualization is significantly easier to implement than full virtualization. It has often provided useful, robust virtual machines, capable of supporting important applications. Partial virtualization has proven highly successful for sharing computer resources among multiple users.
However, in comparison with full virtualization, its drawback is in situations requiring backward compatibility
or portability
. It can be hard to anticipate precisely which features have been used by a given application. If certain hardware features are not simulated, then any software using those features will fail.
is called a "hypercall" in TRANGO
and Xen
; it is implemented via a DIAG ("diagnose") hardware instruction in IBM's CMS
under VM
(which was the origin of the term hypervisor). Examples include IBM's LPAR
s, Win4Lin 9x
, Sun's Logical Domains
, z/VM
, and TRANGO.
s; other examples include Solaris Containers
, OpenVZ
, Linux-VServer
, AIX Workload Partitions
, Parallels Virtuozzo Containers, and iCore Virtual Accounts
.
(DR) plan is good business practice for a hardware virtualization platform solution. DR of a virtualization environment can ensure high rate of availability during a wide range of situations that disrupt normal business operations. Continued operations of VMs is mission critical and a DR can compensate for concerns of hardware performance and maintenance requirements. A hardware virtualization DR environment will involve hardware and software protection solutions based on business continuity needs.
Hardware virtualization DR methods:
Tape backup for software data long-term archival needs : This common method can be used to store data offsite but can be a difficult and lengthy process to recover your data. Tape backup data is only as good as the latest copy stored. Tape backup methods will require a backup device and ongoing storage material.
Whole-file and application replication : The implementation of this method will require control software and storage capacity for application and data file storage replication typically on the same site. The data is replicated on a different disk partition or separate disk device and can be a scheduled activity for most servers and is implemented more for database-type applications.
Hardware and software redundancy : This solution provides the highest level of disaster recovery protection for a hardware virtualization solutions providing duplicate hardware and software replication in two distinct geographic areas.
Virtualization
Virtualization, in computing, is the creation of a virtual version of something, such as a hardware platform, operating system, a storage device or network resources....
of computer
Computer
A computer is a programmable machine designed to sequentially and automatically carry out a sequence of arithmetic or logical operations. The particular sequence of operations can be changed readily, allowing the computer to solve more than one kind of problem...
s or 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...
s. It hides the physical characteristics of a computing platform from users, instead showing another abstract computing platform. At its origins, the software that controled virtualization was called a "control program", but nowadays the terms "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...
" or "virtual machine monitor" are preferred.
Concept
The term "virtualization" was coined in the 1960s to refer to a virtual machineVirtual machine
A 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...
(sometimes called "pseudo machine"), a term which itself dates from the experimental IBM M44/44X
IBM M44/44X
The IBM M44/44X was an experimental computer system from the mid 1960s, designed and operated at IBM's Thomas J. Watson Research Center at Yorktown Heights, New York. It was based on an IBM 7044 , and simulated multiple 7044 virtual machines , using both hardware and software. Key team members were...
system. The creation and management of virtual machines has been called "platform virtualization", or "server virtualization", more recently.
Platform virtualization is performed on a given hardware platform by host software (a control program), which creates a simulated computer environment, a virtual machine (VM), for its guest software. The guest software is not limited to user applications; many hosts allow the execution of complete operating systems. The guest software executes as if it were running directly on the physical hardware, with several notable caveats. Access to physical system resources (such as the network access, display, keyboard, and disk storage) is generally managed at a more restrictive level than the host processor and system-memory. Guests are often restricted from accessing specific peripheral devices, or may be limited to a subset of the device's native capabilities, depending on the hardware access policy implemented by the virtualization host.
Virtualization often exacts performance penalties, both in resources required to run the hypervisor, and as well as in reduced performance on the virtual machine compared to running native on the physical machine.
Reasons for virtualization
- In the case of serverServer (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"...
consolidation, many small physical servers are replaced by one larger physical server to increase the utilization of costly hardware resources such as CPU. Although hardware is consolidated, typically OSs are not. Instead, each OS running on a physical server becomes converted to a distinct OS running inside a virtual machine. The large server can "host" many such "guest" virtual machines. This is known as Physical-to-VirtualPhysical-to-VirtualPhysical-to-Virtual describes the process of decoupling and migrating a physical server's operating system , applications, and data from a physical server to a virtual machine guest hosted on a virtualized platform.-Manual P2V:...
(P2V) transformation.
- A virtual machine can be more easily controlled and inspected from outside than a physical one, and its configuration is more flexible. This is very useful in kernel development and for teaching operating system courses.
- A new virtual machine can be provisioned as needed without the need for an up-front hardware purchase.
- A virtual machine can easily be relocated from one physical machine to another as needed. For example, a salesperson going to a customer can copy a virtual machine with the demonstration software to his laptop, without the need to transport the physical computer. Likewise, an error inside a virtual machine does not harm the host system, so there is no risk of breaking down the OS on the laptop.
- Because of the easy relocation, virtual machines can be used in disaster recoveryDisaster recoveryDisaster recovery is the process, policies and procedures related to preparing for recovery or continuation of technology infrastructure critical to an organization after a natural or human-induced disaster. Disaster recovery is a subset of business continuity...
scenarios.
However, when multiple VMs are concurrently running on the same physical host, each VM may exhibit a varying and unstable performance, which highly depends on the workload imposed on the system by other VMs, unless proper techniques are used for temporal isolation among virtual machines
Temporal isolation among virtual machines
Temporal isolation or performance isolation among virtual machine refers to the capability of isolating the temporal behavior of multiple VMs among each other, despite them running on the same physical host and sharing a set of physical resources such as processors, memory, and...
.
There are several approaches to platform virtualization.
Examples of virtualization scenarios:
Running one or more applications that are not supported by the host OS : A virtual machine running the required guest OS could allow the desired applications to be run, without altering the host OS.
Evaluating an alternate operating system : The new OS could be run within a VM, without altering the host OS.
Server virtualization : Multiple virtual servers could be run on a single physical server, in order to more fully utilize the hardware resources of the physical server.
Duplicating specific environments : A virtual machine could, depending on the virtualization software used, be duplicated and installed on multiple hosts, or restored to a previously backed-up system state.
Creating a protected environment: if a guest OS running on a VM becomes damaged in a way that is difficult to repair, such as may occur when studying malware
Malware
Malware, short for malicious software, consists of programming that is designed to disrupt or deny operation, gather information that leads to loss of privacy or exploitation, or gain unauthorized access to system resources, or that otherwise exhibits abusive behavior...
or installing badly-behaved software, the VM may simply be discarded without harm to the host system, and a clean copy used next time.
Full virtualization
In full virtualization, the virtual machine simulates enough hardware to allow an unmodified "guest" OS (one designed for the same instruction setInstruction set
An instruction set, or instruction set architecture , is the part of the computer architecture related to programming, including the native data types, instructions, registers, addressing modes, memory architecture, interrupt and exception handling, and external I/O...
) to be run in isolation. This approach was pioneered in 1966 with the IBM CP-40 and CP-67
CP-67
CP-67 was the control program portion of CP/CMS, a virtual machine operating system developed for the IBM System/360-67 by IBM's Cambridge Scientific Center. It was a reimplementation of their earlier research system CP-40, which ran on a one-off customized S/360-40...
, predecessors of the VM
VM (operating system)
VM refers to a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers. The first version, released in 1972, was VM/370, or officially Virtual Machine Facility/370...
family. Examples outside the mainframe field include Parallels Workstation
Parallels Workstation
Parallels Workstation is the first commercial software product released by Parallels, Inc., a developer of desktop and server virtualization software...
, Parallels Desktop for Mac
Parallels Desktop for Mac
Parallels Desktop for Mac by Parallels, Inc., is software providing hardware virtualization for Macintosh computers with Intel processors.-Overview:Parallels, Inc...
, VirtualBox
VirtualBox
Oracle VM VirtualBox is an x86 virtualization software package, originally created by software company Innotek GmbH, purchased by Sun Microsystems, and now developed by Oracle Corporation as part of its family of virtualization products...
, Virtual Iron
Virtual Iron
Virtual Iron Software, was located in Lowell, Massachusetts, sold proprietary software for virtualization and management of a virtual infrastructure...
, Oracle VM
Oracle VM
Oracle VM is the server virtualization offering from Oracle Corporation. Oracle VM is based on the open-source Xen hypervisor technology, supports Windows, Linux, and Oracle Solaris guests and includes an integrated Web based management console. Oracle VM features fully tested and certified Oracle...
, Virtual PC
Microsoft Virtual PC
Windows Virtual PC is a virtualization program for Microsoft Windows. In July 2006 Microsoft released the Windows-hosted version as a free product...
, Virtual Server
Virtual server
Virtual server may refer to:* Virtual private server, a method of server hosting using virtual machines.* Virtual hosting, a method that servers such as webservers use to host more than one domain name on the same computer....
, Hyper-V
Hyper-V
Microsoft Hyper-V, codenamed Viridian and formerly known as Windows Server Virtualization, is a hypervisor-based virtualization system for x86-64 systems. A beta version of Hyper-V was shipped with certain x86-64 editions of Windows Server 2008, and the finalized version was released on June 26,...
, VMware Workstation
VMware Workstation
VMware Workstation is a virtual machine software suite for x86 and x86-64 computers from VMware, a division of EMC Corporation, which allows users to set up multiple x86 and x86-64 virtual machines and use one or more of these virtual machines simultaneously with the hosting operating system...
, VMware Server
VMware Server
VMware Server is a free-of-charge virtualization-software server suite developed and supplied by VMware, Inc....
(formerly GSX Server), KVM
Kernel-based Virtual Machine
Kernel-based Virtual Machine is a virtualization infrastructure for the Linux kernel. KVM supports native virtualization on processors with hardware virtualization extensions....
, QEMU
QEMU
QEMU is a processor emulator that relies on dynamic binary translation to achieve a reasonable speed while being easy to port on new host CPU architectures....
, Adeos
Adeos
Adeos is a nanokernel hardware abstraction layer or a hypervisor that operates between computer hardware and the operating system that runs on it. It is distinct from other nanokernels, in that it is not just a low level layer for an outer kernel...
, Mac-on-Linux
Mac-on-Linux
Mac-on-Linux is an open source virtual machine program for running Mac OS on PowerPC computers running Linux. It can also be used to run another instance of another PowerPC-based operating system ....
, Win4BSD, Win4Lin Pro
Win4Lin
Win4Lin was a proprietary software application for Linux which allowed users to run a copy of Microsoft Windows 95, 98, Me, 2000 or XP applications on their Linux desktop.-Overview:...
, and Egenera
Egenera
Egenera, Inc. is a multinational converged infrastructure technology company with corporate headquarters in Marlborough, Massachusetts in the United States. Egenera designs, manufactures, and sells blade servers as well as converged infrastructure management software, and offers consulting and...
vBlade technology.
Hardware-assisted virtualization
In hardware-assisted virtualization, the hardware provides architectural support that facilitates building a virtual machine monitor and allows guest OSes to be run in isolation. Hardware-assisted virtualization was first introduced on the IBM System/370 in 1972, for use with VM/370, the first virtual machine operating system. In 2005 and 2006, Intel and AMD provided additional hardware to support virtualization. Sun Microsystems (now Oracle CorporationOracle Corporation
Oracle Corporation is an American multinational computer technology corporation that specializes in developing and marketing hardware systems and enterprise software products – particularly database management systems...
) added similar features in their UltraSPARC T-Series processors in 2005. Examples of virtualization platforms adapted to such hardware include Linux KVM
Kernel-based Virtual Machine
Kernel-based Virtual Machine is a virtualization infrastructure for the Linux kernel. KVM supports native virtualization on processors with hardware virtualization extensions....
, VMware Workstation
VMware Workstation
VMware Workstation is a virtual machine software suite for x86 and x86-64 computers from VMware, a division of EMC Corporation, which allows users to set up multiple x86 and x86-64 virtual machines and use one or more of these virtual machines simultaneously with the hosting operating system...
, VMware Fusion
VMware Fusion
VMware Fusion is a virtual machine software product developed by VMware for Macintosh computers with Intel processors. Fusion allows Intel-based Macs to run x86 and x86-64 "guest" operating systems, such as Microsoft Windows, Linux, NetWare and Solaris as virtual machines simultaneously with Mac OS...
, Microsoft Hyper-V, Microsoft Virtual PC
Microsoft Virtual PC
Windows Virtual PC is a virtualization program for Microsoft Windows. In July 2006 Microsoft released the Windows-hosted version as a free product...
, Xen
Xen
Xen is a virtual-machine monitor providing services that allow multiple computer operating systems to execute on the same computer hardware concurrently....
, Parallels Desktop for Mac
Parallels Desktop for Mac
Parallels Desktop for Mac by Parallels, Inc., is software providing hardware virtualization for Macintosh computers with Intel processors.-Overview:Parallels, Inc...
, Oracle VM Server for SPARC
Logical Domains
Logical Domains is the server virtualization and partitioning technology from Sun Microsystems released in April 2007. It has been re-branded as Oracle VM Server for SPARC since Oracle Corporation completed the acquisition of Sun in January 2010. Each domain is a full virtual machine with a...
, VirtualBox
VirtualBox
Oracle VM VirtualBox is an x86 virtualization software package, originally created by software company Innotek GmbH, purchased by Sun Microsystems, and now developed by Oracle Corporation as part of its family of virtualization products...
and Parallels Workstation
Parallels Workstation
Parallels Workstation is the first commercial software product released by Parallels, Inc., a developer of desktop and server virtualization software...
.
Hardware platforms with integrated virtualization technologies include:
- x86 (and x86-64)X86 virtualizationIn computing, x86 virtualization is the facility that allows multiple operating systems to simultaneously share x86 processor resources in a safe and efficient manner, a facility generically known as hardware virtualization...
—AMD-V (previously known as Pacifica), Intel VT-x (previously known as Vanderpool)- IOMMUIOMMUIn computing, an input/output memory management unit is a memory management unit that connects a DMA-capable I/O bus to the main memory...
implementations by both AMD and Intel.
- IOMMU
- Power ArchitecturePower ArchitecturePower Architecture is a broad term to describe similar RISC instruction sets for microprocessors developed and manufactured by such companies as IBM, Freescale, AMCC, Tundra and P.A. Semi...
(IBMIBMInternational Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
, Power.orgPower.orgPower.org is an organization whose purpose is to develop, enable and promote Power Architecture technology. The objective is to establish open standards, guidelines, best practices and certifications regarding Power Architecture, as well as drive adoption of the platform.Power.org was founded in...
) - Virtage (HitachiHitachiHitachi 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...
) - UltraSPARC T1UltraSPARC T1|right|262px|UltraSPARC T1 processorSun Microsystems' UltraSPARC T1 microprocessor, known until its 14 November 2005 announcement by its development codename "Niagara", is a multithreading, multicore CPU...
, T2, T2+UltraSPARC T2Sun Microsystems' UltraSPARC T2 microprocessor is a multithreading, multi-core CPU. It is a member of the SPARC family, and the successor to the UltraSPARC T1. The chip is sometimes referred to by its codename, Niagara 2...
, SPARC T3 (Oracle CorporationOracle CorporationOracle Corporation is an American multinational computer technology corporation that specializes in developing and marketing hardware systems and enterprise software products – particularly database management systems...
)
In 2006 first-generation 32- and 64-bit x86 hardware support was found rarely to offer performance advantages over software virtualization.
Partial virtualization
In partial virtualization, including address space virtualization, the virtual machine simulates multiple instances of much of an underlying hardware environment, particularly address spaceAddress space
In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity.- Overview :...
s. Usually, this means that entire operating systems cannot run in the virtual machine – which would be the sign of full virtualization
Full virtualization
In computer science, full virtualization is a virtualization technique used to provide a certain kind of virtual machine environment, namely, one that is a complete simulation of the underlying hardware...
– but that many applications can run. A key form of partial virtualization is address space virtualization, in which each virtual machine consists of an independent address space
Address space
In computing, an address space defines a range of discrete addresses, each of which may correspond to a network host, peripheral device, disk sector, a memory cell or other logical or physical entity.- Overview :...
. This capability requires address relocation
Virtual memory
In computing, virtual memory is a memory management technique developed for multitasking kernels. This technique virtualizes a computer architecture's various forms of computer data storage , allowing a program to be designed as though there is only one kind of memory, "virtual" memory, which...
hardware, and has been present in most practical examples of partial virtualization.
Partial virtualization was an important historical milestone on the way to full virtualization. It was used in the first-generation time-sharing system CTSS, in the IBM M44/44X
IBM M44/44X
The IBM M44/44X was an experimental computer system from the mid 1960s, designed and operated at IBM's Thomas J. Watson Research Center at Yorktown Heights, New York. It was based on an IBM 7044 , and simulated multiple 7044 virtual machines , using both hardware and software. Key team members were...
experimental paging system, and arguably systems like MVS
MVS
Multiple Virtual Storage, more commonly called MVS, was the most commonly used operating system on the System/370 and System/390 IBM mainframe computers...
and the Commodore 64
Commodore 64
The Commodore 64 is an 8-bit home computer introduced by Commodore International in January 1982.Volume production started in the spring of 1982, with machines being released on to the market in August at a price of US$595...
(a couple of 'task switch' programs). The term could also be used to describe any operating system that provides separate address spaces for individual users or processes, including many that today would not be considered virtual machine
Virtual machine
A 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...
systems. Experience with partial virtualization, and its limitations, led to the creation of the first full virtualization system (IBM's CP-40
IBM CP-40
CP-40 was a research precursor to CP-67, which in turn was part of IBM's then-revolutionary CP[-67]/CMS – a virtual machine/virtual memory time-sharing operating system for the IBM System/360-67, and the parent of IBM's VM family. CP-40 ran multiple instances of client operating systems...
, the first iteration of CP/CMS
CP/CMS
CP/CMS was a time-sharing operating system of the late 60s and early 70s, known for its excellent performance and advanced features...
which would eventually become IBM's VM family
VM (operating system)
VM refers to a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers. The first version, released in 1972, was VM/370, or officially Virtual Machine Facility/370...
). (Many more recent systems, such as Microsoft 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...
and Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, as well as the remaining categories below, also use this basic approach.)
Partial virtualization is significantly easier to implement than full virtualization. It has often provided useful, robust virtual machines, capable of supporting important applications. Partial virtualization has proven highly successful for sharing computer resources among multiple users.
However, in comparison with full virtualization, its drawback is in situations requiring backward compatibility
Backward compatibility
In the context of telecommunications and computing, a device or technology is said to be backward or downward compatible if it can work with input generated by an older device...
or portability
Porting
In computer science, porting is the process of adapting software so that an executable program can be created for a computing environment that is different from the one for which it was originally designed...
. It can be hard to anticipate precisely which features have been used by a given application. If certain hardware features are not simulated, then any software using those features will fail.
Paravirtualization
In paravirtualization, the virtual machine does not necessarily simulate hardware, but instead (or in addition) offers a special API that can only be used by modifying the "guest" OS. This system call to the hypervisorHypervisor
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...
is called a "hypercall" in TRANGO
Trango Virtual Processors
Trango Virtual Processors is a privately owned company that builds real-time hypervisors and development tools for embedded systems. The company was founded in 2004 by Pierre Coulombeau and Fabrice Devaux. They are headquartered in Grenoble, France. Trango was acquired by VMware in October 2008...
and Xen
Xen
Xen is a virtual-machine monitor providing services that allow multiple computer operating systems to execute on the same computer hardware concurrently....
; it is implemented via a DIAG ("diagnose") hardware instruction in IBM's CMS
Conversational Monitor System
The Conversational Monitor System is a relatively simple interactive computing single-user operating system.* CMS is part of IBM's VM family, which runs on IBM mainframe computers...
under VM
VM (operating system)
VM refers to a family of IBM virtual machine operating systems used on IBM mainframes System/370, System/390, zSeries, System z and compatible systems, including the Hercules emulator for personal computers. The first version, released in 1972, was VM/370, or officially Virtual Machine Facility/370...
(which was the origin of the term hypervisor). Examples include IBM's LPAR
LPAR
A logical partition, commonly called an LPAR, is a subset of computer's hardware resources, virtualized as a separate computer. In effect, a physical machine can be partitioned into multiple logical partitions, each hosting a separate operating system....
s, Win4Lin 9x
Win4Lin
Win4Lin was a proprietary software application for Linux which allowed users to run a copy of Microsoft Windows 95, 98, Me, 2000 or XP applications on their Linux desktop.-Overview:...
, Sun's Logical Domains
Logical Domains
Logical Domains is the server virtualization and partitioning technology from Sun Microsystems released in April 2007. It has been re-branded as Oracle VM Server for SPARC since Oracle Corporation completed the acquisition of Sun in January 2010. Each domain is a full virtual machine with a...
, z/VM
Z/VM
z/VM is the current version in IBM's VM family of virtual machine operating systems. z/VM was first released in October 2000 and remains in active use and development . It is directly based on technology and concepts dating back to the 1960s, with IBM's CP/CMS on the IBM System/360-67...
, and TRANGO.
Operating system-level virtualization
In operating system-level virtualization, a physical server is virtualized at the operating system level, enabling multiple isolated and secure virtualized servers to run on a single physical server. The "guest" OS environments share the same OS as the host system – i.e. the same OS kernel is used to implement the "guest" environments. Applications running in a given "guest" environment view it as a stand-alone system. The pioneer implementation was FreeBSD jailFreeBSD Jail
The FreeBSD jail mechanism is an implementation of operating system-level virtualization that allows administrators to partition a FreeBSD-based computer system into several independent mini-systems called jails....
s; other examples include Solaris Containers
Solaris Containers
Solaris Containers is an implementation of operating system-level virtualization technology for x86 and SPARC systems, first released publicly in February 2004 in build 51 beta of Solaris 10, and subsequently in the first full release of Solaris 10, 2005.It is present in newer OpenSolaris based...
, OpenVZ
OpenVZ
OpenVZ is an operating system-level virtualization technology based on the Linux kernel and operating system. OpenVZ allows a physical server to run multiple isolated operating system instances, known as containers, Virtual Private Servers , or Virtual Environments...
, Linux-VServer
Linux-VServer
Linux-VServer is a virtual private server implementation that was created by adding operating system-level virtualization capabilities to the Linux kernel. It is developed and distributed as open source software.The project was started by Jacques Gélinas...
, AIX Workload Partitions
Workload Partitions
AIX Workload partitions are a software implementation of operating system-level virtualization technology introduced in the IBM's AIX 6.1 operating system that provides application environment isolation and resource control....
, Parallels Virtuozzo Containers, and iCore Virtual Accounts
ICore Virtual Accounts
iCore Virtual Accounts is free download OS level virtualization for Microsoft Windows XP.-Program:The program is an isolated virtual machine that runs on top of the existing hardware and operating system...
.
Hardware virtualization disaster recovery
A disaster recoveryDisaster recovery
Disaster recovery is the process, policies and procedures related to preparing for recovery or continuation of technology infrastructure critical to an organization after a natural or human-induced disaster. Disaster recovery is a subset of business continuity...
(DR) plan is good business practice for a hardware virtualization platform solution. DR of a virtualization environment can ensure high rate of availability during a wide range of situations that disrupt normal business operations. Continued operations of VMs is mission critical and a DR can compensate for concerns of hardware performance and maintenance requirements. A hardware virtualization DR environment will involve hardware and software protection solutions based on business continuity needs.
Hardware virtualization DR methods:
Tape backup for software data long-term archival needs : This common method can be used to store data offsite but can be a difficult and lengthy process to recover your data. Tape backup data is only as good as the latest copy stored. Tape backup methods will require a backup device and ongoing storage material.
Whole-file and application replication : The implementation of this method will require control software and storage capacity for application and data file storage replication typically on the same site. The data is replicated on a different disk partition or separate disk device and can be a scheduled activity for most servers and is implemented more for database-type applications.
Hardware and software redundancy : This solution provides the highest level of disaster recovery protection for a hardware virtualization solutions providing duplicate hardware and software replication in two distinct geographic areas.
See also
- Virtual applianceVirtual applianceA virtual appliance is a virtual machine image designed to run on a virtualization platform ....
- 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...
- Desktop virtualizationDesktop virtualizationDesktop virtualization , as a concept, separates a personal computer desktop environment from a physical machine using the client–server model of computing....
- Comparison of platform virtual machines
- Dynamic infrastructureDynamic InfrastructureDynamic Infrastructure is an information technology paradigm concerning the design of data centers so that the underlying hardware and software can respond dynamically to changing levels of demand in more fundamental and efficient ways than before...
- Popek and Goldberg virtualization requirementsPopek and Goldberg virtualization requirementsThe Popek and Goldberg virtualization requirements are a set of conditions sufficient for a computer architecture to support system virtualization efficiently. They were introduced by Gerald J. Popek and Robert P. Goldberg in their 1974 article "Formal Requirements for Virtualizable Third...
- PhysicalizationPhysicalizationPhysicalization, the opposite of virtualization, is a way to place multiple physical machines in a rack unit.It can be a way to reduce hardware costs, since in some cases, server processors cost more per core than energy efficient laptop processors, which may make up for added cost of board level...