On Mon, 31 Oct 2011, Cotton, Randall wrote:
Well, I simply don't have enough disks yet to fill up a single raid group per node. 80 disks, 6 nodes.
Is there a reason you bought so many filers and so few disks? It seems to me that management would have been much simpler (and this whole situation could have been avoided, in fact) with one filer. 80 spindles is nothing to a single filer head, let alone a clustered filer.
Right, though I understand from conventional wisdom that the gains diminish to tiny increments past about 16 data disks per aggregate (and your exposure to a failed disk and long reconstruction times becomes big enough that going past 16 may not be worth it).
You're conflating aggregates and raid groups again.
The performance within a single raid group isn't much different after 16 disks. The rebuild time for a single disk is the same regardless of raid group size. The chances of a double-disk failure within a single raid group go up a bit with larger raid groups.
However, in an *aggregate*, the more spindles you have (that is, the more raid groups, since you want to add full raid groups when you can), the better the performance, and it does keep going up because the I/O spreads out more and more as you go to very wide stripes.
-Adam