Hello, I'm in the process of evaluating OpenVZ vs Xen. I must say that I'm leaning towards Xen at this point, but I want to give OpenVZ a fair chance. One thing I'm a bit unclear on... I know that (obviously) the CTs run the same kernel as CT0. Can I migrate a CT to a node with a different kernel? How are kernel upgrades done on OpenVZ (without downtime)? Thanks, Jason
You can live migrate the containers from a machine with the older kernel to a machine with the newer kernel, we maintain backward compatibility. In most cases you can also migrate from newer to older, but this is not guaranteed since sometimes (say few times a year) we change the dump file format and can not maintain forward compatibility. I haven't heard about a single case when this was an issue though. So yes you can do kernel updates w/o stopping containers that way -- migrate all CTs to another box, update the kernel and migrate all CTs back. Another way is to use ksplice. As for Xen vs OpenVZ, check out HP labs paper from 2007 comparing Xen and OpenVZ -- http://www.hpl.hp.com/techreports/2007/HPL-2007-59R1.html