-----Original Message----- From: Adam Levin [mailto:levins@westnet.com] Sent: Monday, October 31, 2011 10:29 AM To: Cotton, Randall Cc: toasters@teaparty.net Subject: RE: Is there a graph somewhere of performance vs raid group size?
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.
No argument there. There are 3 separate geographical sites, though, and HA was desired everywhere. For what it's worth, I was brought on after the purchase.
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.
Ooh, yes, quite correct. 16 disks per raid group, not aggregate, is what I meant. Thanks for correcting that.
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.
This is an important distinction and though I'm not able to afford the luxury yet of multiple aggregates per node, it's an excellent point to make and keep in mind.
Thanks Randall