No - my mistake. I know what you mean. So really is it not worth me mirroring the drives? What if I put the OS on one drive and the virtual machines on another drive? Then look at backup solutions? Or stick it all on one drive and get some backup software to back it up to the second drive? Or should I just bite the bullet and backup to a seperate NAS box? As you can guess I'm new to this virtual stuff. Our main fileserver gets backed up across the broadband network every night with the files being sent to LEA Towers. It's been a long time since I had to worry about AIT3/4 tape backups on our RM DCs :-)
I'm sure others will point out that mirroring is not a backup - delete a file on one half of the mirror and the mirroring system quickly and effciently deletes it on the other half, too. If by "mirroring" you mean RAID of some description then that's a good start, but ideally you should have some kind of diasaster recovery facility (server conks out, how do you restore it / get another to take over) and file/email/etc backup so people can restore stuff they delete by accident.
I thought about looking at the Zen stuff but the Physical to Virtual application costs some money (not sure how much). The heartbeat sounds interesting as well. Will research that tomorrow.
My experience is with Linux servers, in which case you install DRBD to mirror harddrives between two machines (like having a RAID-1 array split over separate machines) and have the second machine take over the running of the VM should the first one stop for some reason. You can do that manually, or use Hearbeat to do automatic failover for you. Some VM systems will also transfer live, running VMs between different physical machines for you, but as a failover solution for a school this is probably overkill - a service coming back up a few minutes after a server fails while a new VM boots is generally perfectly acceptable.