Leveraging vSAN for Highly Available Management Clusters : Use Case Architecture : 4.3 Witnesses and Witness Host : 4.3.3 Witness Host and Virtual Appliance Sizing
   
4.3.3 Witness Host and Virtual Appliance Sizing
For the physical witness host, the resource sizing requirements are met by the minimum ESXi host requirements.
For the witness host appliance, the resource sizing depends on the configuration selected during the OVA deployment (see the following table).
The sizing requirement for this architecture example is small to normal, depending how many virtual machines are loaded into the CMP. A normal configuration for the witness host appliance is recommended for the current scenario of a management cluster.
Table 3. Witness Host Appliance Sizing
Deployment Model
Configurations
Tiny (10 VMs or fewer)
2 vCPUs, 8 GB vRAM, 8 GB ESXi boot disk, one 10-GB SSD, one 15-GB HDD
Supports a maximum of 750 witness components
Normal (up to 500 VMs)
2 vCPUs, 16 GB vRAM, 8 GB ESXi boot disk, one 10-GB SSD, one 350-GB HDD
Supports a maximum of 22,000 witness components
Large (more than 500 VMs)
2 vCPUs, 32 GB vRAM, 8 GB ESXi boot disk, one 10-GB SSD, one 350-GB HDD
Supports a maximum of 45,000 witness components