Confused about sys.dm_io_virtual_file_stats num_of_reads/writes column
The latency of of the I/O system (which the average latency per IOPS is an indicator of) tell you if you are adding more load on the I/O system than it can handle. Because of this, the average latency, when compared with the media you are running on provides a good indicator as to whether I/O is the problem or not.

As a rule of thumb, here are the latencies you should expect if you are not overloaded on the I/O system


Spinning media: Around 5-10ms
SSD: &lt;1ms


If you are seeing latencies higher than that, you know that the I/O system is being asked to do more work than it can handle