On 2011 Nov 2, at 2:28 , Adam Levin wrote:
On Tue, 1 Nov 2011, Cotton, Randall wrote:
Unfortunately, I've not been enlightened as to performance numbers for varying small aggregate sizes with one raid group, so I guess I'll have
Yeah, sorry about that, but it appears we just don't have that information available to us (and NetApp reps don't seem to want to answer :) ).
My guess is that it's not very different from most other RAID setups. There's a nice IOPS calculator for random raid setups here: http://www.wmarow.com/strcalc/strcalc.html
raw-disk-IOPS are roughly linear in the number of data drives. So one 10 disk raid-DP array (8 data disks) will be twice as fast as one 6 disk raid-DP array (4 data disks). At least in raw disk IOPS.
Of course, if your working set is small enough that most if it fits in cache, and you have a nice cache hit rate of, say, 90% (not unusual), the number of read IOPS is roughly multiplied by 10.
And... because of WAFL, netapp writes are generally extremely efficient, compared to random RAID writes. At least if your aggregates aren't too full.
You will have to google for your drive characteristics: mainly the drive seek latency.
And then, the netapp head will likely add a nice IO queue to the mix, getting even more IOPS out of your array.
And of course, your read/write ratio will make a difference too... although for netapps, certainly not as big as the wmarow.com site wants you to believe (in fact, because of the WAFL layout and NVRAM, writes might even be faster than reads. That of course assumes that your NVRAM is big enough).
And since I'm not a netapp engineer, there are probably other factors that influence the number of IOPS that a netapp produces, that I'm not aware of. Netapp does publish benchmarks for most of their storage systems, but these are usually based on benchmarks with LOTS of drives, so the netapp head itself is pushing its limits. With just a few dozen disks as the OP has, the netapp head won't be the limiting factor for any configuration.
So to summarise, I'm not surprised netapp doesn't give performance numbers for the situations like you described, since there are simply too many factors in play for a realistic comparison.