Double Parity in ZFS
The development of ZFS doesn´t stands still. In Opensolaris Build 41 you will find double parity RAID, or in marketing lingo: RAID 6. Adam Leventhal summarizes RAID-6 in ZFS in his weblog.
Adam Leventhal notes one additional thing, why ZFS is the last word in Filesystem:
What's especially cool about ZFS is that we don't just blithely reconstruct data, but we can verify it against the known checksum. This means, for example, that we could get back seemingly valid data from all disks, but fail the checksum; in that case we'd first try reconstructing each individual block, and then try reconstructing every pair of blocks until we've found something that checksums. You can see the code for combinatorial reconstruction here.