4.3.1 Witness Host
With a two-node cluster, as in this example, the minimum configuration still requires a third node as witness, hosting exclusively metadata, but not data.
The witness host for a vSAN is supported using two different deployment models:
• A physical server with ESXi host installed.
• A special appliance containing a virtual ESXi host deployed as virtual machine (nested ESXi).
In either case, the witness host (physical or virtual appliance) is dedicated to one vSAN cluster. It cannot be shared with more than one cluster.