RAID iOPS Calculator - iOPS Required for Array Workload To calculate the iOPS required by an array supporing a given read/write workload, enter the total iOPS needed, the read workload (which will provide the write workload), and the RAID level being used (so IO penalty can be accounted for). Then, click the Calculate Usable RAID Capacity button.
The IOPS of Cache is HUGE, so the easiest way would be to take the remaning percentage, e.g., the cache-miss ratio, and divide your IOPS by that. For example, if you array sustains 1000 IOPS and you estimate a 90% cache-miss ratio, you could bump up your IOPS estimate to 1,111 IOPS.
When you create a DB instance, you specify the IOPS rate and the size of the volume. The ratio of IOPS to allocated storage (in GiB) must be at least 0.5 (1.0 on RDS for SQL Server) and not more than 50. Amazon RDS provides that IOPS rate for the DB instance until you change it.
This is a heavily transactional database type, so we'll assume a 50:50 read-write ratio. A single 2.5" 15K SAS drive should be able to achieve about 250 IOPS. To achieve this without cache, you would then need sixteen spindles. That is, 16*250 = 4000 read IOPS and 2000 write IOPS; at 50:50 that's 3000 IOPS.