for 'classical storage', potential IOP limits tend to be something like

Drive type Maximum recommended IOPS per drive
SAS Flash (all types) 20,000
SAS 15K 350
SAS 10K 250
NL-SAS 150

with RAID type co-efficient.

For Isilon the above does not apply as node type needs to be taken into account.

So how do I calculate the max IOP capability of an isilon array.

Presumably its also complicated by directories being pinned to different tiers, ie if I have  multiple F* nodes and H* nodes and pinned directory x to H* nodes, then theoretical IOP capability of F* nodes is irrelevant other than saying directories pinned to F* nodes do not consume H* nodes theoretical IOPs ?