22.7. Troubleshooting Storage Problems

Many factors affect storage subsystem performance. If bus or controller bandwidth is too narrow, read/write requests will be delayed and the disk drives might be underutilized as a result. If the drives themselves are too slow, read/write responses will be delayed. If both bandwidth and the drives are experiencing excessive utilization, the overall system is approaching saturation. Excessive page file hits can reduce the I/O bandwidth needed for other transactions. If an array controller is present, its read/write priority and stripe-size setting can also have an effect. The type and speed of the drive are also factors.

22.7.1 Evaluating the Storage Subsystem

Two useful counters in the PhysicalDisk category of performance objects are % Disk Time and Average Disk Queue Length.

The % Disk Time counter indicates the percentage of elapsed time that the selected disk drive is busy servicing read or write requests.

The Average Disk Queue Length indicates the average number of both read and write requests that were queued for the selected disk during the sample interval.