What is the function of the vSAN Witness appliance in a stretched VI Workload Domain?

In a stretched vSAN cluster within a VMware Cloud Foundation (VCF) VI Workload Domain, the vSAN Witness appliance serves as a quorum mechanism. It is deployed as a third site to help the cluster determine which site should continue operating in the event of a network partition or site failure. This third "witness" site does not store actual data but maintains metadata to track the cluster's status, ensuring high availability and preventing data loss by enabling failover between the two primary data sites.

The vSAN Witness does not store a third copy of VM data, provide additional storage, or act as a network connection during outages.