Witness appliance displaying alarms "Host with vSAN service enabled is not in the vCenter cluster" and "Host cannot communicate with one or more of the nodes in the vSAN Stretched Cluster"

Products

• VMware vSAN

Issue/Introduction

• In a Stretched vSAN Cluster, when a Witness appliance is placed inside a cluster, you may see a warning:
  • "Host with vSAN service enabled is not in the vCenter cluster"
  • "Host cannot communicate with one or more of the nodes in the vSAN Stretched Cluster"
• The cluster where the Witness is placed is not the same cluster with which it is configured.
• Placing the witness host in this unsupported configuration (vSphere cluster membership) prevents it from functioning as a vSAN witness.  
• This could result in data unavailability or loss in the event that a physical node suffers a failure before the condition is corrected.

Environment

VMware vSAN 6.x

VMware vSAN 7.x

VMware vSAN 8.x

Cause

These alarms are triggered because the Witness Appliance should not be inside of any kind of cluster.

The witness should be part of the Datacenter.

The witness should not be deployed inside the 2-node or Stretched cluster it's going to be a part of.

 

In the below image witness3.demo.local is a vSAN Witness Appliance which is placed inside the cluster, this is wrong.

witness.demo.central, witness1.demo.local, witness2.demo.local and witness4.demo.local are vSAN Witness Appliances which are placed under the Datacenter, this is correct.

 

 

Resolution

These alarms can be fixed by moving the Witness Appliance to the root of the datacenter. 

To move the Witness Appliance to the root of the datacenter:

Precheck: Make sure all the VMs are running with a valid vSAN Storage Policy, and the objects are compliant with the storage policy.

1. Disable the stretched cluster from Cluster > Configure > Fault Domains & Stretched Cluster
2. Place the witness appliance in maintenance mode.
3. Move the witness appliance to the root of the datacenter.
4. Take the witness appliance out of maintenance mode.
5. Re-enable the stretched cluster from Cluster > Configure > Fault Domains & Stretched Cluster

Additional Information

Understanding the vSAN Witness Host
Details and setup of the vSAN Witness Appliance