I tried to get AuFS working again, and finally got it running.
It looks like after each reboot I need to run #insmod /lib/modiules/2.6.25.5-1.1-xen/kernel/fs/aufs.ko
This loads the aufs mofule into the kernel?

Without it each #mount command responded with “aufs is not a known fs type” (or something like that.