Don't do it!
This post was intented as praise for Xen and Ubuntu. I even created a screenshot to go with it. However, after trying to run Xen on Hardy, I am a little disappointed in Ubuntu.
The screenshot shows virtual machines (VMs) running Windows Server 2003, FreeBSD and Linux on a single cheap consumer-grade PC.
Unfortunately, shortly after the screenshot was taken the machine crashed.
We have been running a Xen server for about 2 and a half years now.
Initially we compiled the Xen kernel ourselves on a machine running Dapper Drake LTS and we were very happy about it. Shortly after Feisty came out we decided to try and take advantage of the packaging system provided by Ubuntu. This required a small Xen downgrade, but we were still quite happy, and the machine ran without problems for about 2 years. Unfortunately Feisty doesn't come with the 5 year support, so we needed to upgrade. We didn't have the time to upgrade to Hardy right away. Lucky us! Now we could wait until a nasty networking bug got fixed.
Using a Fresh Hardy install and some workarounds
- rename Xen bridge (fair enough)
- rename /lib/tls to /lib/tls.disabled (bug?)
- use losetup -r /dev/loop0 /media/isos/jeos-8.04.2-jeos-i386.iso and use phy:/dev/loop0 in config (bug?)
- fix grub on each linux VM
- ditch the Windows VM
we finally got our virtual machines running again and I was able to take the screenshot.
But shortly thereafter the machine crashed. And it kept crashing ever since. We have tried to determine the cause of the crashes for some time. We tried running only a single virtual machine, but it still crashed. Even running without virtual machines it still crashed. Every single time a single process (usually, but not always qemu-dm) grabs 100% CPU. But we couldn't get a hold on what exactly was going wrong.
In the end we switched to KVM. This turned out to be pretty easy. Since we were using hvm guests stored on LVM partitions we could use the old VMs (no modification needed). And the VMs lived happily ever after...