Another Xen Annoyance
I really do like Citrix’s XenServer, despite my moaning earlier about it’s barely-functional snapshotting capabilities.
Rather more disappointing is the fact that it’s completely floored by the arrival of a new distro version. Specifically, there is (understandably) no ‘template’ for Centos 5.4 -and if you try using the supplied template for Centos 5.3 hoping to slip in the incremental release without too much fuss, you’re in for a big disappointment: the virtual machine loses contact with its source DVD and demands a driver be supplied before it can continue reading from it. No such driver can be supplied, so that’s the end of that. Using a template for an OS installation is important, because it allows the VM guest to be properly paravirtualised. If you try and cook your own (using the Other Install Media template), the installation will succeed, but you won’t benefit from a properly xen-ified kernel and hence performance of the VM will be sub-optimal (posh language for ‘pretty crap’).
The only mechanism I’ve really got to work, in fact, is to create a new VM using the Centos 5.3 template, install Centos 5.3, and then do a yum update so that Centos itself takes care of the business of migrating to version 5.4. No problem if you have unlimited downloads on your broadband link, I suppose… but not exactly an ideal way to go.
I would hope that Citrix would regularly release new templates that could be downloaded and installed… but their forums are full of dark talk of ‘wait until the next release of XenServer next year’. That seems a crazy way of going about things. Despite having put XenServer into production use at work, I think I am going to have to re-evaluate it if it can’t do snapshotting or new distro upgrades properly.