Hi Ronak8590,
The Servicedesk Implementation guide has suggested IOPS for Servicedesk customers, and this is a great starting point for Workflow users. I have attached the document, and the IOPS measurements are on page 51. The entire scalability chapter (and actually all of the planning pages) would be good to review.
Your workflows will in large measure determine the IOPS you will need. But the measurements in the document are a great starting place.
The Disk Reads/Sec and Disk Writes/Sec Perfmon counters for LogicalDisk are the IOPS counters to review.
Thanks