I'm really looking for something that will cluster the filesystem across multiple nodes for both enhanced performance and redundancy, sort of RAID 1+0 over TCP. There is already a Windows DFS "cluster" on-site that does this (hence the questions about Samba - I'm not sure whether the MS Unix Services will serve a DFS and I'd trust Samba over Microsoft's implementation of NFS), but I'd rather have a linux-only setup for Moodle (

).
DRBD wasn't ideal as
IMO it "wastes" a node when the cluster is fully operational; since Intermezzo isn't ready for production use, I'm thinking of giving PVFS (Parallel Virtual File System Version 2) a go which seems to do this and more, unless you can provide any more good ideas

.
Thanks everyone for all the help!
BTW The Performance pages in the Moodle wiki are still lacking on the topic of clustering...