Information regarding vSphere storage device latency performance metrics (2001676)
Performance metrics for VMware vSphere storage may appear to spike higher when performing storage operations comprised of commands that take significantly longer to complete than the median latency.
This article provides information regarding storage device latency performance metrics.
The vSphere performance metrics made available by
resxtop and the vSphere Client are averages over the sample timeframe. Measurements snapshots are taken at the end of each sample timeframe, and values averaged, and the resulting value reported as the average value within that range.
Working with Performance Statistics section of the vSphere Datacenter Administration Guide
Performance Monitoring Utilities: resxtop and esxtop section of the vSphere Resource Management Guide for your version of vSphere.
If the sampled metric consists of a non-homogeneous set of data, metrics may be skewed in unexpected ways.
The measured average of storage latency over a sample window varies significantly depending on how many other commands are completing at the same time, even though these examples depict only a single command which is taking a long time to complete:
- 4 commands completed in 1ms and 1 command completed in 500ms implies an average latency of 100.8ms.
- 9 commands completed in 1ms and 1 command completed in 500ms implies an average latency of 50.9ms.
- 19 commands completed in 1ms and 1 command completed in 500ms implies an average latency of 25.95ms.
Note: Consider what is being measured when evaluating averages of any sampled performance metric before drawing any conclusions based on those metrics.
For information related to this topic, see Performance Analysis Methods Technical Note.