In the Virtual Volumes environment, fault domains define how specific replication groups must be combined when being replicated from a source to a target site.
Fault domains are configured and reported by the storage array, and are not exposed in the vSphere Client. The Storage Policy Based Management (SPBM) mechanism discovers fault domains and uses them for validation purposes during a virtual machine creation.
For example, provision two virtual machines, one associated with replication group Anaheim: B, the second associated with replication group Anaheim: C. SPBM validates the provisioning because each VM is in its own replication group with corresponding target fault domains.
Now provision two VMs, one associated with replication group Anaheim: B, the second associated with replication group Anaheim: D. This configuration is invalid. Both replication groups replicate to the New-York fault domain, however, only one replicates to the Boulder fault domain.