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, and it can contain only witness components.

The workflow to deploy and configure the vSAN witness appliance includes this process.

When you deploy the vSAN witness appliance, you must configure the size of the witness supported by the vSAN stretched cluster. Choose one of the following options:
  • Tiny supports up to 750 components (10 VMs or fewer).
  • Medium supports up to 21,833 components (500 VMs). As a shared witness, the Medium witness appliance supports up to 21,000 components and up to 21 vSAN two-node clusters.
  • Large supports up to 45,000 components (more than 500 VMs). As a shared witness, the Large witness appliance supports up to 24,000 components and up to 24 vSAN two-node clusters.
  • Extra Large supports up to 64,000 components (more than 500 VMs). As a shared witness, the Extra Large witness appliance supports up to 64,000 components and up to 64 vSAN two-node clusters.
Note: These estimates are based on standard VM configurations. The number of components that make up a VM can vary, depending on the number of virtual disks, policy settings, snapshot requirements, and so on. For more information about witness appliance sizing for vSAN two-node clusters, refer to the vSAN 2 Node Guide.

You also must select a datastore for the vSAN witness appliance. The witness appliance must use a different datastore than the vSAN stretched cluster datastore.

  1. Download the appliance from the VMware website.
  2. Deploy the appliance to a vSAN host or cluster. For more information, see Deploying OVF Templates in the vSphere Virtual Machine Administration documentation.
  3. Configure the vSAN network on the witness appliance.
  4. Configure the management network on the witness appliance.
  5. Add the appliance to vCenter Server as a witness ESXi host. Make sure to configure the vSAN VMkernel interface on the host.