Virtualization and Linux--A Primer
The Xen Hypervisor
Carla Schroder
Thursday, December 7, 2006 12:40:38 PM
The Xen hypervisor is the new darling of the virtualization crowd. In case you were wondering, hypervisor (or sometimes virtual machine monitor) is the host system that supervises concurrent guest operating systems. Naturally, this is too cool to be merely a supervisor, so it's a hypervisor.
Xen operates in two ways: in software, or with hardware support. Xen's paravirtualization runs modified guest operating systems to achieve near-native performance. Open source operating systems like Linux, the BSDs and OpenSolaris already have Xen ports to run as guests. Several Linux distributions, NetBSD/xen, and OpenSolaris are available as ready-made Xen hosts in varying stages of polish.
As you've doubtless already noticed, certain major non-Unix operating systems are left out of the paravirtualization party. The team that developed Xen created a Microsoft Windows port under an academic license, but due to licensing restrictions cannot release it. But this doesn't matter if you have the right Intel or AMD CPU and Xen 3.0. Intel's Vanderpool and AMD's Pacifica are CPU instruction sets that allow unmodified guest operating systems to run side-by-side. Pretty slick stuff.
If the host operating system is compromised, or someone steals the physical machine, well, you're pretty much doomed. Even fancy new virtualization technologies can't help you.
Ease of administering virtualized systems depends on the implementation. Provisioning in some virtualization applications is fast and easy, and you can move operating systems and applications around freely. This translates into fast failure recovery, less maintenance downtime, and easy scaling, both up and down. Next week we'll look at some of pros and cons of some of the different virtualization applications for Linux.
Resources
This article originally appeared on Enterprise Networking Planet, a JupiterWeb site.
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