An accurate way to examine or monitor the disk usage (busy) time is to measure disk latencies. Typically, if the value of one of the following counters is larger than 20 ms, the disk is over-loaded:
- Avg. Disk sec/Read
- Avg. Disk sec/Write
- Avg. Disk sec/Transfer
There are several other values you can use to monitor disk performance, and this topic is described in detail in Chapter 30 - Examining and Tuning Disk Performance, of the Windows 2000 Professional Resource Kit
, and TechNet monthly CD-ROMs also have this chapter. However, it is important to note that the %Disk Time description there incorrectly states a registry key to clamp the values at %100 exists as that would be misleading.