Question: I know what the reads per second and writes per second counters are, but what are the seconds per read and seconds per write counters for? When should I be using the seconds per read and seconds per write counters for?
Answer:The two sets of counters are very different. The reads per seconds and writes per seconds counters show how many IO reads or writes are sent from the Windows OS to the storage subsystem. The seconds per reads and seconds per writes counters show the amount of time that it takes for the IO operation to get from the storage to the Windows OS (in the case of reads) or from the Windows OS to the storage (in the case of writes).
This additional set of counters is very important when looking at performance problems. If you are only looking at the number of IO which are going through from the server to the storage you don't have all the information. You may see a slowdown in the number of IO between the server and the storage, but if you don't know if the IO are being processed slower than before you won't know why the number of IO per second have slowed down. If on the other hand you see the number of IO being processed per second lower than normal as well as the number of seconds per IO going up then odds are there is a performance problem on the storage array that needs to be resolved.
Hopefully this helps in your storage performance troubleshooting.