This counter of the System object is an indicator of the number of outstanding requests the processor has in its queue. Each application thread requires a certain number of processor cycles. A consistent processor queue length greater than 2 may mean the processor is inadequate for the applications that it runs.

These counters of the Logical Disk object monitor the average number and the instantaneous number of both reads and writes queued for the selected disk.

Tip    For best performance, Avg. Disk Queue Length should not exceed two requests per disk drive.

These counters of the Logical Disk object monitor the percentage of time spent servicing the particular I/O requests during the sampling interval. Use the % Disk Time counter in conjunction with the % Processor Time counter of the Processor object to determine the time the system spends executing I/O requests or processing non-idle threads. Use the % Disk Read Time and % Disk Write Time counters to gain further insight into the type of I/O being performed. Your goal is to have a high percentage of time spent executing non-idle threads (high % Processor Time) and executing I/O (high % Disk Time). On a highly optimized system, these counters can be consistently over 90 percent. If one of these counters is substantially lower than the other, it is likely that the high counter indicates a bottleneck, and further investigation is necessary. With high % Disk Time, use the % Disk Read Time and % Disk Write Time counters to get the I/O breakdown. With high % Processor Time, use the % User Time and % Privileged Time to get further CPU utilization breakdown.