But DRBD is a way of keeping volumes in sync, not so much a file system.
The easiest FS to administer that I know of is sshfs. I use it heavily and it is stable and actually very fast. It can beat NFS even sometimes.. And all you need is Openssh server running and a fuse support in the client. The ssh server is the real gauge on how well sshfs works. Anything other then a relatively recent version of OpenSSH and I doubt the results will be that good.
But if DRBD was even being considured then your needs are going to be specialized. Other alternative to look at could possibly be Redhat's GNBD from GFS or ISCSI.