A vSAN witness appliance, or a physical host, can be used for the witness function. The vSAN witness appliance includes licensing, while a physical host must be licensed accordingly.

A vSAN witness appliance is provided with each release of vSAN. The underlying vSphere version is the same as the version running vSAN. Upon initial deployment of the vSAN witness appliance, it is required to be the same as the version of vSAN.

Deploying the witness for a normal configuration requires 10 GB of cache storage. The physical host does not require flash or an SSD device. The capacity device must be 350 GB or greater. Traditional spinning drives are enough because the witness will mark those devices as needed.

Table 4.      Witness sizing

Note: Use the calculator in Error! Reference source not found. to determine whether the size of the appliance is sufficient.

Each vSAN stretched-cluster configuration requires a witness host. The witness must reside on a third site that has independent paths to each data site. While the witness host must be part of the same vCenter as the hosts in the data sites, it must not be on the same cluster as the data site hosts. Network Address Translation (NAT) is not supported.

Note: The witness host OVA file includes a license; it does not consume a vSphere license. However, a physical host requires a vSphere license.

Witness host requirements

• A witness host cannot be part of any vSAN enabled cluster
• Have at least one VMkernel adapter with vSAN traffic enabled
• The adapter must be connected to all hosts in the stretched cluster