Average Disk Seconds Per Write (Logical Disk)

Summary

The Avg. Disk sec/Write (LogicalDisk\Avg. Disk sec/Write) for the logical disk has exceeded the threshold. The performance of applications that rely on this logical disk may be negatively impacted as the disk is taking an unusually long time to service write requests.

The Avg. Disk sec/Write counter indicates how fast data is being written on average for a specific logical disk.

Causes

A high Avg. Disk sec/Write performance counter value may occur due to a burst of disk write requests by either an operating system or application.

Resolutions

To view recent history for the Logical Disk\Avg. Disk sec/Write performance counter you can use the following view:

Start Logical Disk Avg. Disk Sec/Writes Performance View

To increase the available storage subsystem throughput for this logical disk, do one or more of the following:

• Upgrade the controllers or disk drives.

• Switch from RAID-5 to RAID-0+1.

• Increase the number of actual spindles.

Be sure to set this threshold value appropriately for your specific storage hardware. The threshold value will vary according to the disk’s underlying storage subsystem. For example, the “disk” might be a single spindle or a large disk array. You can use MOM overrides to define exception thresholds, which can be applied to specific computers or entire computer groups.

Additional

The Avg. Disk sec/Writes counter is useful in gathering throughput data. If the average time is long enough, you can analyze a histogram of the array’s response to specific loads (queues, request sizes, and so on). If possible, you should observe workloads separately.

You can use throughput metrics to determine:

• The behavior of a workload running on a given host system. You can track the workload requirements for disk write requests over time. Characterization of workloads is an important part of performance analysis and capacity planning.

• The peak and sustainable levels of performance that are provided by a given storage subsystem. A workload can either be used to artificially or naturally push a storage subsystem (in this case, a given logical disk) to its limits. Determining these limits provides useful configuration information for system designers and administrators.

However, without thorough knowledge of the underlying storage subsystem of the logical disk (for example, knowing whether it is a single spindle or a massive disk array), it can be difficult to provide an optimized one size fits all threshold value.

You must also consider the Avg. Disk sec/Writes counter in conjunction with other write request characteristics (for example, request size and randomness/sequentially) and the equivalent counters for write disk requests.

If the Avg. Disk sec/Writes counter is tracked over time and if it increases with the intensity of the workloads that are driving the write requests, it is reasonable to suspect that the logical disk is saturated if throughput does not increase and the user experiences degraded system throughput.

For more information about storage architecture and driver support, see the Storage - Architecture and Driver Support Web site at http://go.microsoft.com/fwlink/?LinkId=26156.