Current Disk Queue Length (Physical Disk)

Summary

The physical disk has had a consistently high value for the “Current Queue Length” counter over multiple consecutive samples. As a result, I/O requests latency will most likely increase on this physical disk.

Current Disk Queue Length is the number of requests outstanding on the disk at the time the performance data is collected. This means that the physical disk is not able to honor I/O requests as fast as they are being made.

Causes

Either the physical disk has recently experienced a significant increase in activity, and this spike has resulted in exceeding the threshold, or physical disk’s utilization has been steadily increasing over time and has finally reached a point of going over the threshold.

The other possibility is that some portion of the underlying physical disks or the disk subsystem is malfunctioning or misconfigured, impairing the performance of the physical disk.

Resolutions

To further investigate the issue consider the following:

• Review the System event log on the system, to see if there are any error indicating problems with the physical disk, physical disks or the storage sub-system.

• Review the history of current queue length for this physical disk using either performance views or reports in Operations Manager or the performance monitor. This will help in determining if the issue has started recently or if the activity has been steadily increasing over a longer period of time.

• Review the other performance counters for the physical disk such as “Disk Bytes/sec”, “Disk Reads/sec” and “Disk Writes/sec” to understand what types of I/O are driving the overall disk utilization.

• Review the “Process” performance counters such as “IO Data Operations/sec” to identify which processes are contributing most significantly to the overall I/O on the system. Once the top processes are identified the “IO Read Operations/sec” and “IO Write Operations/sec” counters will help in further in determining the type of I/O that the process is doing.

Based on the findings from further investigation, resolutions may vary and could include one of the following:

• Address any issues or misconfigurations with the storage sub-system.

• Scale back the rate of I/O occurring on the system or distribute the workload across more physical disks.

• Upgrade the drives or storage sub-system to handle the increased load.

• If the increased load is acceptable then the threshold of the monitor can be changed to be less restrictive. Likewise the number of consecutive samples can be increased to force the monitor to only change state when utilization is sustained over longer periods of time.