Back in the R100 days it was *required* to spread the volumes, in a very specific order, vertically across shelves (volumes at that time were the aggregates of today). The logic is still sound from a performance view, but keep in mind that if your spares are spread randomly every time you lose a drive your perfect drive configuration degrades.
However, look at your current IO requirements and decide. Shelves today have 24 15k drives in them with 3Gb or more on the loop. You need an awful lot of to saturate that. Certainly it can be done but if you're filer is generally hovering around 20k ops or a couple hundred MB throughput, it's unlikely you're going to saturate any single new shelf. Let alone if that IO is over multiple shelves.
If you're talking about DS14's, the numbers drop notably of course but the same logic applies. Maybe with those numbers drop to 8k ops or 50MB throughput. Not sure.
With multi-pathing the odds of losing a loop completely are very, very low. Personally I just let WAFL decide where to grab drives from; haven't cared about that level of control for a long time now...
Jeff Kennedy Qualcomm, Incorporated QCT Engineering Compute 858-651-6592
-----Original Message----- From: owner-toasters@mathworks.com [mailto:owner-toasters@mathworks.com] On Behalf Of Ray Van Dolson Sent: Thursday, April 07, 2011 12:58 PM To: toasters@mathworks.com Subject: Distribute aggregate across shelves or limit to one shelf?
Best practice (based on my reading of the archives) seems to be to distribute disk membership in an aggregate across disk shelves.
This would appear to be for performance reasons primarily (less chance of saturating a shelf's "uplink" to the controller), but how does it affect reliability?
If I limit myself to one aggregate per shelf, if I lose that shelf I lose only the one aggregate. If aggregates are distributed I could lose all of them.
My thought is that the chance of the shelf failing is actually pretty slim as its hardware isn't all that sophisticated.
And obviously there are performance penalties for limiting to one aggregate per shelf (disk count maximums).
Thanks, Ray