How many spares?

[garyn_87048]

I have recently built a mini home system, raidz2, with five 3TB drives resulting in about 7TB ZFS pool. I have added a sixth drive as a spare. The cabinet has room for eight drives.

Does the forum have a recommendation for the number or ratio of spare drives?

If experience says zero, then I'm okay pooling everything, meanwhile, having three drives (all the remaining spots in my case) would seem excessive.?.?

Looking for tips from the experts!!!

Thanks!

 

[jgreco]

Ideally, with warm spares, you build RAIDZ levels first.

RAIDZ1 plus a spare should really be a RAIDZ2 pool
RAIDZ2 plus a spare should really be a RAIDZ3 pool
RAIDZ3 plus a spare is the first point at which a spare can't be part of the running pool

This is basically a matter of how valuable your data is to you. RAIDZ1 is risky because you've lost redundancy after virtually any issue; a disk read error means you're relying on the other drives for the same block, and loss of a disk means you lose redundancy and any additional errors are unrecoverable. RAIDZ2 is sufficient for general redundancy for most people. If a disk fails, you still have redundancy and can slot in a new drive. RAIDZ3 improves upon that and is suggested for large pools where loss of the pool would be "bad." Some of us do RAIDZ3 with a spare.