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Performance diagnostics in vSAN reports: "The increase in latency in the vSAN stack might be beyond expected limits” (2150018)

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In the vSAN performance diagnostics, you see this message:

The increase in latency in the vSAN stack might be beyond expected limits.


This issue occurs because the latency observed in the virtual machine is higher than the latency observed in vSAN backend disks.  The detailed performance graphs show the latencies at both layers (VM layer and vSAN diskgroup layer) for each host in the cluster. Write and read latency is separated.


To resolve this issue, use one of these options:
  • Congestion: Often, the increase in latency may be correlated with disk group congestion. Congestion is a feedback mechanism to slow down the rate of incoming IO requests from the higher layers of vSAN. When congestion is encountered, upper layers of vSAN queue more requests, and this leads to higher latency at the VM layer. For more information on how to address vSAN congestion, see  vSAN is experiencing congestion in one or more disk groups .

  • Network issues: A network issue, such as large packet losses, large number of duplicate ACKS, retransmissions, and so on in the network can lead to large number of retransmissions of IO requests in the VSAN stack. Many network issues are caused by misconfiguration of switch VLAN policies, or NIC teaming policies. Investigate this issue further.

See Also

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