VMware supports both physical ESXi hosts and a virtual appliance as a vSAN witness host. VxRail 4.7.100 supports using the vSAN witness virtual appliance as a vSAN witness host only.

The vSphere license is included and hard coded in the witness virtual appliance. The witness virtual appliance does not consume additional vSphere licenses and does not require a dedicated physical host. Starting with vSAN 7 update 1 (VxRail release 7.0.132), the witness can be shared with up to 64 2-node vSAN deployments.

Note: The witness VMware ESXi OVA host deploys a Virtual Standard Switch (vSS). For details, see the VMware documentation.

Software requirements

The VxRail 2-node cluster requirements are as follows:

• vSAN witness appliance version 6.7u1 or later is required.
• The witness appliance version must be the same vSAN version that is configured on the ESXi hosts.
• 2-node VxRail clusters and stretched clusters require Dell Professional Services engagement

Installation

Witness appliance installation requirements are as follows:

• The witness appliance must be installed, configured, and added to the VCenter inventory before deployment of the vSAN 2-node cluster on VxRail.
• The witness appliance must connect to both vSAN nodes.
• The witness vSAN traffic must be on a different vLAN than the data node’s witness traffic.
• The witness appliance must be managed by the same VCenter Server that is managing the 2-node cluster.
• For VxRail versions 7.0.100 and earlier, a witness appliance can only be connected to one vSAN 2-node cluster. In VxRail 7.0.132 and later versions, a single witness can be shared with up to 64 2-node clusters.
• The witness can run in the same physical site as the vSAN data nodes. However, it cannot be placed in the 2-node cluster to which it provides quorum.
• The general recommendation is to place the vSAN witness host in a different data center, such as a main data center or a cloud provider.
• It is possible to deploy the witness appliance on another 2-node cluster, but it is not recommended. A VMware RFQ is required for this solution design.

Sizing

• During deployment, you can select from four typical sizes (tiny, normal, large, and extra-large) for a witness appliance. Each option has different requirements for compute, memory, and storage. Select the appropriate size from the deployment drop-down menu. The general recommendation is to use the normal size. However, 2-node clusters with up to 25 VMs are good candidates for the “Tiny” option because they are less likely to reach or exceed 750 components.
• Each storage object is deployed on vSAN as a RAID tree, and each leaf of the tree is a component. For instance, when we deploy a VMDK with a RAID 1 mirror, we will have a replica component in one host and another replica component in another host. The number of stripes that are used has an effect. For example, if using two stripes, we will have two replica components in each host.