Configuring Stretched Cluster Results in "A specified parameter was not correct - Witness host already configured in stretched cluster"

Products

• VMware vSAN

Issue/Introduction

Impact/Risks:

• Can't reconfigure the stretched cluster.
• Objects in a Reduced availability state.

Symptoms:
vCenter shows that a stretched cluster is not configured, but when you try to configure it and add the witness you get the error: Configuring Stretched Cluster Results in "A specified parameter was not correct - Witness host already configured in stretched cluster"

Environment

VMware vSAN (All Versions)

Cause

This can occur when the witness is not removed properly when wanting to replace it. Especially during upgrades.
 

For example, instead of disabling the stretched cluster, the witness is simply removed from inventory. 

Resolution

To get around this error, log into RVC, see KB Ruby vSphere Console (RVC)

(Note: If  unknowledgeable on how to use RVC or are not comfortable with doing so, please open up an SR with vSAN Support)

Once in the RVC console navigate to the cluster and use the following command: 

vsan.stretchedcluster.witness_info . 

Example: 
/localhost/Datacenter/computers/vSAN_Cluster> vsan.stretchedcluster.witness_info .
Found witness host for vSAN stretched cluster.
+------------------------+--------------------------------------+
| Stretched Cluster      | vSAN_Cluster                         |
+------------------------+--------------------------------------+
| Witness Host           | HostSystem("host-120748")            |
| Witness Host UUID      | 626172e0-7723-656a-bfde-############ |
| Preferred Fault Domain | Primary                         |
| Unicast Agent Address  | 10.20.0.70                           |
+------------------------+--------------------------------------+
=======================================================

You should see the witness that vSAN thinks should be in the cluster. 

You can then remove that witness via the following command:

vsan.stretchedcluster.remove_witness .

Example:
/localhost/Datacenter/computers/vSAN_Cluster> vsan.stretchedcluster.remove_witness .
Found witness host for vSAN stretched cluster.
+------------------------+--------------------------------------+
| Stretched Cluster      | vSAN_Cluster                         |
+------------------------+--------------------------------------+
| Witness Host           | HostSystem("host-120748")            |
| Witness Host UUID      | 626172e0-7723-656a-bfde-############ |
| Preferred Fault Domain | Primary                                  |
| Unicast Agent Address  | 10.20.0.70                           |
+------------------------+--------------------------------------+
Removing witness host from the cluster...
Task: Remove witness host
New progress: 30%
Task result: success
=======================================================

Now re-configuration of the stretched cluster with the new witness should work successfully. 

Additional Information

How to Login into RVC?