Unable to add Witness node to vSAN stretch cluster with error "The witness host must not be part of a vSAN enabled cluster"

Products

• VMware vSAN

Issue/Introduction

When attempting to select a witness host during vSAN stretch cluster configuration you get error "The witness host must not be part of a vSAN enabled cluster"

 

The witness is in use by a vSAN cluster, but does not appear in use per vCenter and is not a Shared Witness

• Running esxcli vsan cluster get on the witness shows it is in a cluster
  • This could be 'Stand alone' where vSAN was enabled before but did not join into a cluster, or is currently contributing to a vSAN cluster, but vCenter is unaware of its contribution. 

 

If it is already part of the vSAN cluster, but vCenter does not see it under fault domains, you may see a similar health alert like this, stating 'host connectivity' 

Environment

vSAN

Cause

The witness is already has a vSAN cluster (either stand alone or part of another vSAN cluster), where vCenter may not be aware of that of the cluster it is joined to. 

Resolution

1: Place witness into maintenance mode (with: no data migration). 

2: On SSH / CLI, to the witness node, run the command: esxcli vsan cluster leave

3: Confirm the witness is no longer part of any cluster and shows 'clustering disabled'. Run the command: esxcli vsan cluster get

4: On vCenter, attempt to configure the witness again under the fault domain tab from that cluster.