Analyzing disk performance by using Windows Performance Monitor (perfmon)

Examine disk statistics by using performance counters that are available in the Performance Monitor.

1. Start Performance Monitor. From a command prompt, enter: perfmon.
2. Create a Data Collector Set to collect data about disks. Select the following performance counters from the Physical Disk category:
   • Avg. Disk Sec./Transfer
   • Avg. Disk Queue Length
   • Avg Disk Bytes/Transfer
   • Disk Bytes/sec
   • Split IO/sec
3. Run perfmon tool while you are experiencing the performance problem. Compare the results with the guidance in the following table.

   Performance counter	Guidance
   Physical Disk: Avg. Disk Sec./Transfer	Values less than 25 ms are good.
   Physical Disk: Avg Disk Queue Length	A value that is 2 or 3 times the number of disks in the array is optimal.
   Physical Disk: Avg Disk Bytes/Transfer	The goal is that the stripe size for the array is at least the average of this counter.
   Physical Disk: Disk Bytes/sec	Optimal result is that the sum of values for all disks that are attached to a single controller is less than 70% of the theoretical throughput.
   Physical Disk: Split IO/sec	A nonzero value for this counter indicates possible disk fragmentation.