Welcome to the dollars for IOPS game !  
Assuming a 20ms response time threshold - 15K RPM SAS can deliver 220 IOPS vs SATAs 44 IOPS  (about 5x)
So SAS will get you the IOPS your VMs need.

You should also check out where your IOPs are being spent - are you doing any snap mirror operations?  de-dup?


Also which VMs are hogging the IOPs?  You can download a free trial of vCenter Operations and see via the VM IO heat maps which VMs might be moved to local disk on the ESXi hosts (to offload the netapp)

good luck - would like to hear how it turns out!

On May 21, 2012, at 10:12 PM, James Andrewartha wrote:

Hi,

We have a small metrocluster with 2TB SATA disks in DS14mk2 trays,
mostly used for VMware. We desperately need more IOPs, and are tossing
up another 14x2TB SATA tray, which would have the benefit of just
expanding the aggregate, vs 12 of 600GB 15krpm SAS (half a DS4243),
which would give more IOPs but be more admin overhead since we'd have to
move VMs amongst the shelves.

Capacity isn't a problem, and when we built the metrocluster the ATTO
6500N fibre bridge wasn't available, so SATA was our only option at the
time. We're getting quotes for both options, but does anyone have an
opinion on expanding the SATA aggregate vs setting up a new SAS one?

Thanks,

--
James Andrewartha
Network & Projects Engineer
Christ Church Grammar School
Claremont, Western Australia
Ph. (08) 9442 1757
Mob. 0424 160 877
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