Latency reported for virtual machines in vSAN Cluster

Products

• VMware vSAN

Issue/Introduction

Symptom:

Virtual machines running on the vSAN cluster reported high latency at the client layer.

Guest OS and application may see slowness and accessibility issues.

Environment

VMware vSAN 7.x

VMware vSAN 8.x

Cause

This issue may show up when underlying disks on hosts experiencing latency issue.

On vSAN cluster ESXi host, this can be validated by running esxtop and look for the device stats by pressing 'u' after running esxtop, it would report the DAVG and would be causing the latency on vSAN cluster and VMs.

Example screen as below: esxtop and press 'u'

Resolution

As this needs investigation from the hardware vendor, please involve hardware vendor to investigate the elevated DAVG values on the physical disks.

Since the hardware layer reporting the latency, fixing the latency issue at the hardware layer would address the performance issue at the virtual machine layer.