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7 April 2009

Virtualization primer 3: example products

By Andrew Clifford

There are a large number of virtualization products, with no single dominant vendor.

Last week I outlined the three main approaches to virtualization of servers and PCs: hosted hypervisors, OS-level virtualization, and native hypervisors. This week I will briefly cover some of the best-known examples of each.

VMware is one of the leading virtualization companies, and have been providing virtualization solutions for more than 10 years.

VMware Workstation is a Windows or Linux-based hosted hypervisor. It allows one or more guest operating systems to run on a PC. It can be used for testing, to support legacy applications, or special application requirements. VMware Workstation is a paid-for product, though not particularly expensive.

VMware Fusion is a similar product for Intel-based Macs.

VMWare Server is a free hosted hypervisor for Linux or Windows servers. VMware ESXi is a native hypervisor for larger deployments, and has been released as a free product relatively recently.

VMware Infrastructure is a more complete enterprise-level solution.

Virtuozzo from Parallels is an OS-level virtualization product. This takes a fundamentally different approach to virtualization. Instead of running multiple operating system instances on one physical server, it cuts a single operating system instance into multiple "containers", each one of which then behaves as if it were an independent server. There are Virtuozzo solutions for both Windows and Linux.

Because all the containers share resources, Virtuozzo allows many containers to be packed onto a single server. Parallels claims that it is possible to support thousands of containers on one physical server. Virtuozzo can provide a good environment for consolidating a large number of independent servers onto a small number of physical platforms.

Parallels also provides native hypervisor products and hosted hypervisor products. They support the open source product OpenVz, which is used as the basis for Virtuozzo, but which has more limited features.

Xen is a leading open-source native hypervisor, supported by many large technology companies. Xen is used as the basis of commercial offerings from Citrix, Oracle and Sun.

The Xen hypervisor runs on the physical hardware and runs many separate operating system instances (guests). One of the guests is used to control the virtualization and to provide drivers for the other guests. By separating the drivers from the hypervisor, Xen can support many different virtualization options. It can support both Windows and Linux guests, though Windows is only supported on the more recent Intel and AMD chips that include specific support for virtualization.

Xen is built in to many Linux distributions and can simply be switched on as an option during installation.

This is just a selection of some of the leading products. All the major technology providers, including Microsoft and Sun, have a range of virtualization products, bot free and paid-for. There are many more open-source virtualization products, including emulators (QEMU, Bochs), hosted hypervisors (User Mode Linux), OS-level virtualization (Open VZ, Linux VServer), and native hypervisors (Linux kernel-based virtual machine or KVM).

Each provider supports many different virtualization approaches and options. The products are changing rapidly, borrowing ideas and technology from each other, and often changing ownership. This is a rapidly developing area of technology, with no single dominant vendor.

Next: Virtualization primer 4: recommendations


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