1) never cluster unless you have to.
2) never use distributed Filesystems unless you need a global namespace
3) distributed filesystems mean that you have a single point of failure, its just more complex and subtle form of failure.
4) You have to think about how partition works, and how you want to recover.
Sharding standard NFS fileservers is by far the easiest way to scale, have redundancy, and partition your failure zones. using autofs on a custom directory you can mount servers ondemand. /mnt/0 /mnt/1 /mnt/2 etc etc etc.
You then have the ability to chose your sharding scheme for speed, redundancy or some other constraint.
Nowadays the performance that distributed systems allowed are commodity. A single 4u storage server can saturate a 100gig network link with random disk IO.