Given the previous entry , here's my opinions so faron when you should let ZFS handle your redundancy and when you shouldhave your storage backend do RAID. (This assumes that you have a storagebackend; if not, well, you don't have much choice.)

• if you are doing mirroring, you really want to let ZFS handleit because ZFS will do a much better job of handling small problemsthan your storage backend can.

• if you have a SAN and need your frontends to survive temporary

In a comment on my last entry , Matt Simmons asked why you'd let ZFS handleRAID level issues instead of just handling them in your storage backend(SAN or otherwise). Having ZFS do this is the recommended practice, fora number of reasons (some of which the ZFS FAQs will tell you about).

Here's the reasons for letting ZFS handle the RAID stuff that I knowabout (or at least can think of right now):

• ZFS can reliably repair corrupted blocks in mirrors , because

Like many other RAID-oid systems, ZFS has a notion of spare disks;you can add one or more spare disks to a pool, and ZFS will use themas necessary in order to maintain pool redundancy in the face of diskproblems. For details, you can see the zpool manpage.

Well, sort of. Actually, how ZFS handles spare disks is significantlydifferent from how normal RAID systems handle them, and the pleasantlybland and normal description of spares in the zpool manpage elides asignificant number of important