What VM technology to use?

[Paul Gear]

Cary Bielenberg wrote:
> I'm currently knocking up some virtual servers at work, I will be using 
> Hardy x64 on HP DL585 servers (dual amd processors, 16Gb ram etc) I have 
> used the free Vmware server 1.6/Hardy on other boxes but I fell that 
> that performance leaves a lot to be desired. Today I tried KVM but it 
> seems a pig to setup. I want to run 2 x Citrix/Win2k3 on 1 server & 1 x 
> Citrix & 1 x Hardy on the 2nd. What is the consensus to what is a good & 
> intuitive setup VM solution?

I've worked with a number of virtualisation technologies, and what i
believe is that there are no *really* good ones.

If you want to virtualise Windows, nothing comes close to VMware in
terms of functionality.  If you want to run a lot of Linux VMs, VMware
becomes a pain because of having to recompile the stupid VMware drivers
every time you upgrade the kernel.  Also keeping accurate system time is
problematic, although if you run Ubuntu server as guest under an Ubuntu
desktop platform with VMware server, it should do pretty well, due to
the 100 Hz clock that Ubuntu server defaults to.

Xen seems to perform better than VMware for Linux solutions, and
apparently runs Windows OK, too, but the Linux kernel developers hate
it, and therefore you should too.  This is not just a "Linus is my
homeboy" thing, but if the kernel developers hate it, you can expect
problems whenever you upgrade the kernel.

KVM is loved by the kernel developers (evidenced by the fact that it's
integrated with all kernels now), but it still seems Beta quality.  It
certainly hasn't eaten any of the Windows versions i've thrown at it
(including XP and 98), and it didn't co-exist happily with VMware for me.

The one i like best for Linux virtualisation is VServer, since it is
very lightweight.  It works like a chroot on steroids.  Unfortunately,
it requires a patched kernel, which thankfully Debian provides.

So my summary is:
- Windows-centric - use VMware (possibly the new ESXi - haven't tried it)
- Linux-only - try VServer
- best performance in a mixed environment - Xen
- hope for the future - KVM

This article has some useful and brief comparisons:
http://www.shorewall.net/Linuxfest-2008.pdf
And of course there's always the ever-useful Wikipedia - just search for
"comparison of virtual machines" and you're sure to find more
information than you could ever use.

Paul
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