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Troubleshooting vSAN Witness Node Isolation (2150433)

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Symptoms

  • A vSAN Witness Node (Virtual or Physical) is Isolated.
    To confirm witness node isolation run the command: esxcli vsan cluster get 
    If the output of the command returns:
    Sub-Cluster Member Count: 1
    Local Node State: STANDALONE

    Then the Witness is confirmed to be isolated from the vSAN Cluster.

  • The vSAN Witness Host cannot form a Cluster with the remaining vSAN Data Nodes in a Stretched Configuration.
  • Pinging the Witness Host from a vSAN ESXi fails
  • Pinging an ESXi host from a Witness works, but not with a Full TCP Frame

Resolution

In a vSAN Stretched Cluster the Witness plays an important role assuring keeping all the witness components of the vSAN Objects.

To ensure proper TCP/IP communication between the data hosts and the Witness, these requirement exist:
  • Round-Trip Time (RTT) latency between the Witness and the ESXi hosts must be < 500 ms.
  • A full frame must be sent between pings. If using MTU 1500, the payload must be at least 1472. 
  • To verify if the payload can be sent, run this command from one of the ESXi hosts: vmkping -I VSANvmknic WitnessIP -s 1472 -d -c20
    If the ping fails, something on the network is not allowing the full payload to travel between the ESXi and the Witness Host.

  • Static routes must be created on all the ESXi hosts.
    Additional information on how to add static routes to ESXi hosts can be found in the Network Design for Stretched Clusters section in the Administering VMware Virtual SAN guide.

    Note
    : There are no Multicast requirements between the Witness Host and the ESXi hosts
 

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