What does "volume" mean in MAX_IOPS_PER_VOLUME?

Question

When setting MAX_IOPS_PER_VOLUME in a Resource Pool, what exactly does "volume" mean? Specifically, how many "volumes" would be the following cases:

1. Locally attached disk that's split into two partitions E: and F:
2. Software RAID 1 set E: composed of 2 locally attached disks (yes I know software RAID is bad-- adding this case to help me understand SQL Server's definition of "volume", not to design a production setup!)
3. Hardware RAID 1 set E: composed of 2 locally-attached disks
4. SAN disk E: on who knows/who cares how many disks.
5. 1 SQL Server filegroup spread across two locally attached disks E: and F:

I assume the answers to #3 and #4 are "1 volume" and #5 is "2 volumes" but it's #1 and #2 that I'm most curious about.

The specific reason I'm asking is wondering if it's possible to increase the Resource Governor's IOPS limit for locally-attached SSD tempdb while having a lower limit for our SAN data storage.

So I'm wondering if splitting a single physical disk into multiple partitions might be a way to do this, by putting separate tempdb files on each partition so the total tempdb If #1 above makes SQL Server treat one physical disks as multiple volumes for throttling purposes, this may be an option. I'm assuming that this won't work-- that SQL Server is smart enough to know that 2 partitions is one "volume". But was worth asking.

Answer 1

A "volume" is either a drive letter, or a raw partition in SQL Server.

For a resource pool configured for X maximum IOps per volume where a query uses tempdb, splitting that tempdb across multiple volumes on a single physical disk, SSD or not, with the data on a single volume may well give you the granularity you desire. As always, I'd test it.