I don't really see how replication/HA is an issue in this setup beyond normal file system replication/HA (which seems to be a solved "spend money on NAS" problem in the enterprise world). If your filesystem isn't reliable / delivering what's needed then you're gonna have a bad time no matter the storage approach; I doubt some unusual option is involved though it would be cool to be proven wrong.
The only time the filesystem could even potentially have read/write conflicts (assuming 1-to-1 correlation between devices writing to files) is when querying. I did wind up muddling the terminology in the interest of jumping to the actual problem.
