vSphere: 3-sites = two active sites + tie-breaker in 3rd site
Hyper-V: 2-sites = two active sites + tie-breaker in 3rd site
The use of the Metro Availability Witness automates failover decisions in order to avoid split-brain scenarios like network partitions and remote site failures. The witness is deployed as a VM on a third-party server or a Nutanix cluster within a separate failure domain.
The Metro Availability Witness is available for VMware vSphere environments and Microsoft Hyper-V 2016 environments (AOS 5.9 and later).
Nutanix, ECP [HCI]/5.11, Ultimate
SC Configuration, Disaster Recovery, Data Availability