Xen

Xen is an open source hypervisor that provides a paravirtualized architecture. Paravirtualization is a virtualization method where the operating system is modified in order to know that it is virtualized and to take advantage of a standardized virtualization API. More details on paravirtualization are available in our page on Virtualization Methods.

Xen’s requirement for the operating system to be modified makes it difficult to virtualize closed-source operating systems such as Microsoft Windows and even legacy open source operating systems (Linux kernels prior to 2.6, Sun Solaris for x86, etc.).

Xen’s requirement for a modified operating system can be overcome when Intel VT-x capable CPUs are used. Future releases will also support AMD Pacifica CPUs once they are available (early 2006). This support will enable running Microsoft Windows and other legacy operating systems without modification under Xen. When CPU support for virtualization is widely available it is anticipated that paravirtualization will remain the preferred deployment method due to it’s increased performance.

Xen is a single-system hypervisor, it does not support clustering at this time.

The Evolution of Xen

The Xen hypervisor was started as a research project at the University of Cambridge (U.K.) in 2001. Early versions were not used extensively outside of the university and a very small enthusiast group.

Version 2.0 was released in early October 2004, this version saw significantly more testing, it was integrated into some major Linux distributions (SuSE Pro 9.3 being at least one) and it was put to work by a number of ISPs for use in virtual webhosting platforms.

While version 2.0 proved highly usable the demands of enterprise users continued to push Xen forward.

Xen 3.0 was released in December 2005. Version 3 adds support for SMP guest operating systems, PAE and 64bit computing. Version 3 was a major undertaking with much effort expended in ensuring the code remained lean, if not leaner than version 2. Xen 3 continues to offer high performance despite the many added features.

Xen 3 is seeing wide support from hardware manufacturers. Huge contributions were made to Xen development from companies such as AMD, Intel, HP and IBM.

Xen Management

The open source Xen hypervisor provides basic command-line driven management utilities appropriate for managing a single system. For managing virtualization across a larger number of systems the need for higher level tools is apparent.

There are a number of initiatives, both open-source and proprietary, to create high-level tools for enterprise deployment, monitoring, management, etc.

Currently XenOptimizer is available from Xensource. Xensource was founded by Xen’s lead developers and continues to be a hub of development around the Xen hypervisor.

See Xen Community website for more information.