Lustre - no replication (it's on the roadmap for sometime in the next few years), and it relies on access to shared storage (read: FC/iSCSI disk array, and if that fails you loose your data.).
OCFS - no replication, designed for multiple servers accessing one array.
Ceph - has replication, but still in active development, and somewhat complex. Good if you don't mind loosing your data (it's in alpha... if it breaks, you get to keep both pieces...)
GlusterFS - I have no experience with it, but it seems to be pretty stable at this point. And has some degree of replication with is a plus.
If all you're going for is replicated storage across two systems I'd recommend just setting them up separately and rsync'ing from one to the other. Otherwise, one filesystem crash will take out all your data - parallel filesystems can buy you some reliability, but still can't be considered "backup" strategies. And you still need to pay attention to things like RAID (at least RAID6! RAID5 is likely to fall apart after one disk failure with >2 TB disks),
Slashdot Mirror
Lustre - no replication (it's on the roadmap for sometime in the next few years), and it relies on access to shared storage (read: FC/iSCSI disk array, and if that fails you loose your data.). OCFS - no replication, designed for multiple servers accessing one array. Ceph - has replication, but still in active development, and somewhat complex. Good if you don't mind loosing your data (it's in alpha... if it breaks, you get to keep both pieces...) GlusterFS - I have no experience with it, but it seems to be pretty stable at this point. And has some degree of replication with is a plus. If all you're going for is replicated storage across two systems I'd recommend just setting them up separately and rsync'ing from one to the other. Otherwise, one filesystem crash will take out all your data - parallel filesystems can buy you some reliability, but still can't be considered "backup" strategies. And you still need to pay attention to things like RAID (at least RAID6! RAID5 is likely to fall apart after one disk failure with >2 TB disks),