Performance monitor disk counters

To measure latency use: Avg. Disk sec/Write and Avg. Disk sec/Read. The values recorded by these counters are always in seconds (nevermind the scale, scale is used only for the graph). So if the average recorded value for Avg. Disk sec/Write is 0,022 sec it is equal to 22 ms. Latency up to 25 ms is accepted and quite normal

PhysicalDisk\% Idle Time This measures the percentage of time the disk was idle during the sample interval. If this counter falls below 20 percent, the disk system is saturated. You may consider replacing the current disk system with a faster disk system.

Memory\Cache Bytes This indicates the amount of memory being used for the file system cache. There may be a disk bottleneck if this value is greater than 300MB.