Hi MD
IOPS in a NetApp system is a bit of a Dark Art. Whilst the physical disk's IO does come into play you cannot just rely on these numbers for total IO, due the way WAFL writes data in contiguous stripes across a raid group. We also have the fact that dedupe, flexclone, flashcache and flashpool all influence the overall IOPS available, hence when you need to size a NetApp solution SPM is the recommended port of call.
If you have a current system and are worried about IOPS you should look to use Performance advisor which is part of the OnCommand Core package.
