vSAN Health Service - Stretched cluster - Site latency

Products

• VMware vSAN

Issue/Introduction

This article explains the Stretched cluster - Site latency check in the vSAN Health Service and provides details about why it might report an error.

Environment

VMware vSAN 6.x
VMware vSAN 6.5.x
VMware vSAN 6.6.x
VMware vSAN 6.2.x
VMware vSAN 6.7.x

Resolution

Q: What does the Stretched cluster - Site latency health check do?

This test checks the network latency between the fault domains of the two sites and the witness. This health check displays the highest latency among all the host pairs within two fault domains or the witness and verifies that the latency stays within the recommended threshold.

Please refer to the vSAN Stretched Cluster Guide on the threshold for more information about the site latency. This issue has been fixed in 6.0 Patch 3 and later releases.

Q: What does it mean when it is in an error state and how to troubleshoot?

If the test returns a warning or error, it means that the site latency exceeds the threshold of 5msec RTT between sites for a stretched cluster. See the Networking and Latency Requirements for vSAN Stretched Clusters and configure your network so that it meets the recommended requirements.


In order to test from data nodes to witness host the below reference commands can be used:

vmkping -I VSANvmknic WitnessIP -s 1472 -d -c20

vmkping -I vmk1 192.x.x.x -s 1472 -d -c20


For rapid ping test, 1000 pings at fast interval 5ms

vmkping -I vmk1 192.x.x.x -i 0.005 -c 1000                

For more information on vmkping see Testing VMkernel network connectivity with the vmkping command