Real world KVM

We have been using KVM for core servers for ~10 months now. We have ~25 Windows and Linux server VM's on our production cluster of 2 test and 4 production hardware servers (~$3000 each). We even run MSSQL on KVM. Shared storage is on NFS from a couple of DRBD'd storage servers.

When we tested the commercial Citrix Xen offering it could not create a Mandriva or Ubuntu server for us. We have found it much easier to roll VM's with KVM than with Xen. Using a wrapper script and some debconf with Ubuntu's VM builder we can spit out new, updated, Ubuntu server VM's in about 5 minutes custom configured for our environment.

Live migration was far superior for KVM than with VMWare when we tested last summer. KVM allows live migration over SSH (used to be the default mechanism). We see a couple of pings (2 to 5 packets) with increased latency during the infamous migration ping test, compare that to VMWare. We didn't test vs Xen due to the VM creation problem above.

The KVM GUI tools were lacking but were easily overcome with a minimal Perl driven CGI. We even get console in the web browser with a Java VNC applet.

In our study, we eliminated HyperV and Xen early on and it became a contest between VMWare and KVM. KVM won out despite some shortcomings in GUI tools and commercial support. The fact that a VMWare update had a critical bug last summer during our testing influenced our results a bit.