Xen

See also: Xen (Half-Life)

Xen is a Free software of virtualisation, more precisely a hypervisor of virtual Machine.

He is developed by the Université of Cambridge with the the United Kingdom. Xen makes it possible to make function several virtual operating systems (guests) on only one machine host.

Presentation

Xen makes it possible to make turn several operating systems (and their applications) in a way isolated on the same physical machine on platform X86, X86-64, IA-64 and PowerPC (soon on SPARC). The invited operating systems share thus the resources of the machine host.

Xen is a “paravirtualisor” or a “hypervisor” of virtual machines. The invited operating systems are “aware” of subjacent Xen, they need to be “carried” (adapted) to function on Xen. Linux, NetBSD, FreeBSD (bearing in progress) and Plan 9 can now-and-already to function on Xen.

Xen 3 can also make turn of the systems not modified like Windows on processors supporting technology VT.

With technologies Intel Vanderpool and AMD Pacifica this bearing will not be soon necessary any more and all the operating systems will be supported.

Architectures X86, X64, IA-64, PowerPC and SPARC are supported. The multiprocessor (SMP) and partially the Hyper-Threading are supported.

Structure of Xen

Each operating system invited turns in a “field”. Xen is a fine layer functioning directly on the material.

| | | | |- bgcolor=" #CCCCCC" |colspan=" 5" align=" center" | Xen

|- bgcolor=" #EFEFEF" |colspan=" 5" align=" center" | Material: processor, memory, storage, network, etc

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Industrial actors

  • Ian Pratt, the chief of the project, created XenSource, a company dedicated to the development of Xen, its promotion and its support. Investors injected million dollars in this company

  • Red Hat, Projet Fedora, SuSE, Mandriva, Ubuntu Linux, Debian and Gentoo integrated Xen in their distribution
  • AMD announced in February 2005 the integration of material virtualizing technology in its processors 64 bits (AMD64 aka x86-64) under the name of Pacifica code. This material virtualisation is used by Xen version 3.
  • HP announced to dedicate of the contribution resources to the project Xen

  • Citrix Systems, Inc. announced on August 15th, 2007 the aquisition of XenSource, Inc for an amount from approximately $ 500 million. Citrix enters thus the promising market of the virtualisation on the waiters and the work stations.

Comparison with other solutions of virtualisation

Generally, the virtualisation requires an operating system host installed on the material, and optionnellement a transition course. One or more invited operating systems can then be installed in parallel.

  • the software of virtualisation of the type QEMU, VirtualBox, VMWare Workstation/GSX or VirtualPC is complete virtual machines for the invited operating systems, including even a software BIOS (“firmware”). The operating system invited “believes” to turn on a material, but it is “virtual” or “simulated” by the software of virtualisation, invited OS is not “aware” to be virtualized. The overload introduced by the stacking of the operating system host and the virtual machine make of them not very satisfactory solutions for requirements in performance. They are however simplest to implement.

  • the software of virtualisation of the type VMWare ESX allows complete virtual machines for the invited operating systems, including even a bios. But with the difference of the complete virtual machines previously quoted, there is light stacking, the virtual machine rests on a light core named vmkernel. It is an architecture very similar to Xen.

  • the software of the type Chroot, Linux-VServer, OpenVZ or BSD Jail does nothing but isolate certain aspects or resources from the operating system host like the filesystems or the memory capacities. These solutions are very powerful, because of the little of overload (not of stacking of OS host and a software of virtualisation), but the virtualized environments (one cannot speak about machine or virtual operating systems) little or are not completely isolated.

  • User Mode Linux (of acronym UML) is a Linux core compiled to function in memory capacity user (apart from space privileged core). It thus launches out like an application in the operating system host. UML can launch and manage its applications in a way isolated from the other UML which turn on the same machine. Solution far from powerful, because two cores are piled up, it is used especially with the development of the core or the realization of Pot as honey.

Because of this “paravirtualisation” (adaptation of the operating system invited) and of its lightness, Xen is a tool of virtualisation of most powerful.

See too

External bonds

  • Official site of the project
  • XenSource
  • xenfr.org: French-speaking gate of information on the Virtualisation with Linux

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