Friday, January 06, 2012

Windows Disk Performance

The best initial indicator of disk performance on a Windows host is obtained by using the “\Logical Disk(*)\Avg. sec/Read” and “\Logical Disk(*)\Avg. sec/Write” performance monitor counters. These performance monitor counters measure the amount of time that read and write operations take to respond to the operating system. As a general rule of thumb, average response times greater than 15ms are considered sub-optimal. This is based on the typical seek time of a single 7200 RPM disk drive without cache. The use of logical disk versus physical disk performance monitor counters is recommended because Windows applications and services utilize logical drives represented as drive letters wherein the physical disk (LUN) presented to the operating system can be comprised of multiple physical disk drives in a disk array. Use the following rule of thumb when measuring disk latency on the Windows host using the \Logical Disk(*)\Avg. Disk sec/Read or \Logical Disk(*)\Avg. Disk sec/Write performance monitor counters:

1ms to 15ms = Healthy
15ms to 25ms = Warning or Monitor
26ms or greater = Critical, performance will be adversely affected

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