VMware supports both physical ESXi hosts and a virtual appliance as a vSAN Witness host. VxRail v4.7.100 only supports using the vSAN Witness virtual appliance as a vSAN Witness host. The Witness virtual appliance does not consume extra vSphere licenses and does not require a dedicated physical host.
Note: The Witness ESXi OVA host deploys a Virtual Standard witness Switch (vSS). See the VMware documentation for more details.
- vSAN Witness appliance version 6.7u1 or later is required.
- Witness appliance must be at the same vSAN version as the ESXi hosts.
- The vSphere license is included and hard-coded in the Witness virtual appliance.
- The Witness appliance must be installed, configured, and added to vCenter inventory before the vSAN 2-node cluster on VxRail deployment.
- The Witness appliance must have connectivity to both vSAN nodes.
- The Witness appliance must be managed by the same vCenter Server that is managing the 2-node cluster.
- A Witness appliance can only be connected to one vSAN 2-node cluster.
- 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.
- The Witness can run in the same physical site as the vSAN data nodes, but cannot be placed in the 2-node cluster to which it provides quorum.
- It is possible to deploy the Witness appliance on another 2-node cluster, but it is not recommended. A VMware RPQ is required for this solution design.
- Direct-connect configurations require Ports 1 and 2 to be directly connected to the switches. Ports 3 and 4 from Node 1 are directly connected to Ports 3 and 4 of Node 2 respectively.
- Switched configurations require all four ports to be connected to the switch(es).
- There are three typical sizes for a witness appliance that can be selected during deployment: tiny, normal, and large. Each option has different requirements for compute, memory, and storage.
Figure 3. Sizing guidance from the VMware vSAN Planning Guide
- 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 said to be 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 on 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.