Witness VM in Metro Availability Configuration:

A "Witness" is a special VM that monitors the Metro Availability configuration health. The Witness resides in a separate failure domain to provide an outside view that can distinguish a site failure from a network interruption between the Metro Availability sites. It can only be configured on AHV and ESXi hypervisors.

The main functions of a Witness include:

· Making a failover decision in the event of a site or inter-site network failure.
· Avoiding a split-brain condition where the same storage container is active on both sites due to (for example) a WAN failure.
· Handling situations where a single storage or network domain fails.

To learn about the different scenarios you might encounter and the requirements of a witness VM, click here. 

Did you know?
Witness VM can also be deployed if you are using a 2-node cluster! To learn more about how it works in that environment, click here.