The system will only complain if you have no spares left. Based on the fact that you only have 21 disks (10 on one node, 11 on the other?) one spare per node should be plenty.

While double-parity protects you from double disk failure, it doesn’t require you actually have to spares.

From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of Brian.Beaird@cat.com
Sent: Tuesday, October 28, 2008 3:16 PM
To: toasters@mathworks.com
Subject: Nodes Sharing Spares

We are using the IBM n-series filers with our aggregates using dual-parity.  Our filer is a dual-node controller, so each node independently owns different disks from the storage shelves.  My question deals with how spare disks are allocated.  With how it's currently set up, each node has to reserve two disks that it owns as spares to support dual parity.  I don't know that we necessarily need four spares for such a relatively small number of physical disks (21 total).  It seems pretty wasteful to have all that space just sitting there, especially when the chances of more than two disks failing before we can get replacements in are pretty slim.

Is there some way to just let the nodes share a couple spares so that either one can grab them if failures occur in one of their owned disks?  It would be great if I could free up one or two of those spares for actual use.  I know there's a way to force spare disksk into aggregates, but I don't want to do this if that means one node won't have any spares to use.

Thanks,
Brian Beaird