Over one year ago, I tested the then-current versions of KVM, Virtualbox, Xen and VMWare Server in an attempt to identify the best-performing hypervisor (you can find the article here). That tests demonstrated that VMWare Server and Virtualbox where the highest performing softwares, with KVM slightly behind due to slow I/O speed and Xen severely lagging in CPU and memory speed. While the results were surely interesting, I tested the various virtualizer with one guest system only, and I never found the time to run the (desired) multi-guests test.
Now, the free virtualizers landscape is considerably changed: VMWare Server has not been updated since the end of 2009 and now it has some serious problems with the current libc version, while Xen seems a bit “forgotten” by the Linux community. At the same time, KVM and Virtualbox gained considerably traction, and they emerged as the favorite virtualizers in the Linux world.
So, its the time to refresh the current performance status of these two free and open-source virtualizers – in a true, multi-guests environment.