vSphere storage device latency performance metrics
Article ID: 309140
Updated On:
Products
Issue/Introduction
Environment
VMware vCenter Server 4.0.x
VMware vCenter Server 5.1.x
VMware vCenter Server 5.5.x
VMware ESX 4.1.x
VMware vSphere ESXi 6.0
VMware ESXi 3.5.x Embedded
VMware vSphere ESXi 5.5
VMware ESXi 3.5.x Installable
VMware vSphere ESXi 5.1
VMware ESX 4.0.x
VMware vSphere ESXi 5.0
VMware VirtualCenter 2.5.x
VMware ESXi 4.0.x Installable
VMware ESX Server 3.0.x
VMware ESX Server 3.5.x
VMware vCenter Server 4.1.x
VMware vCenter Server 6.0.x
VMware ESXi 4.1.x Embedded
VMware ESXi 4.0.x Embedded
VMware vCenter Server 5.0.x
Resolution
The vSphere performance metrics made available by esxtop, resxtop and the vSphere Client are averages over the sample timeframe. Measurements snapshots are taken at the end of each sample timeframe and values are averaged. The resulting value reported as the average value within that range.
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Working with Performance Statistics section of the vSphere Datacenter Administration Guide
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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.
Measurements of storage device command latency (DAVG/cmd) may generate higher or lower values than expected, if not all commands within the sample complete at the same speed. Most storage device commands complete quickly (< 25ms), but a small number of commands (such as XCOPY, used in VAAI) may take significantly longer to complete.
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 more information, see the Performance Analysis Methods Technical Note.
Additional Information
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