[CentOS] Xen, GFS, GNBD and DRBD?

Hi all,

We're looking at deploying a small Xen cluster to run some of our  
smaller applications. I'm curious to get the lists opinions and advice  
on what's needed.

The plan at the moment is to have two or three servers running as the  
Xen dom0 hosts and two servers running as storage servers. As we're  
trying to do this on a small scale, there is no means to hook the  
system into our SAN, so the storage servers do not have a shared  
storage subsystem.

Is it possible to run DRBD on the two storage servers and then export  
the block devices over the network to the xen hosts? Ideally the goal  
is to have the effect of shared storage on the xen hosts so that  
domains can be migrated between them in case one server needs to go  
offline. Do I run GFS on top of the DRBD mirrored device, exported via  
GNBD to the xen hosts; or the other way around, using GNBD to export  
the DRBD mirrored device and then GFS running on the xen hosts?

Is this possible; is there an easier/simpler/better way to do it?

Thanks,
Tom