Specific vSAN configurations, such as a stretched cluster, require a witness host. Instead of using a dedicated physical ESXi host as a witness host, you can deploy the vSAN witness appliance. The appliance is a preconfigured virtual machine that runs ESXi and is distributed as an OVA file.
Unlike a general-purpose ESXi host, the witness appliance does not run virtual machines. Its only purpose is to serve as a vSAN witness.
The workflow to deploy and configure the vSAN witness appliance includes this process.
Download the appliance from the VMware Web site.
Deploy the appliance to a vSAN host or cluster. For more information, see Deploying OVF Templates in the vSphere Virtual Machine Administration documentation.
Configure the vSAN network on the witness appliance.
Configure the management network on the witness appliance.
Add the appliance to vCenter Server as a witness ESXi host. Make sure to configure the vSAN VMkernel interface on the host.