Joey D’Antoni shows us how to measure IOPs (I/O Per Second) on a SQL Server instance/server:
That handy SQL Server:Resource Pool Stats counter and it’s Disk Read IO/sec and Disk Write IO/sec provide you with the data you need to give your SAN admin. In this screenshot this is an Enterprise Edition instance, and you can see my resource pools on the left side—so if you are using resource governor, you could use this to classify IO workload by application for potential chargeback situations.
Very useful, and when combined with Resource Governor, can help you throttle I/O effectively (as opposed to wildly flailing in the general direction of a fix).