If all the nodes in a vSAN cluster are connected to the same top of the rack (TOR) switch, then the total increase in traffic is only between the primary node and the switch.

If a vSAN cluster spans more than one TOR switch, traffic between the switch expands. If a cluster spans many racks, multiple TORs form Fault Domains (FD) for the rack awareness. The primary node sends N messages to the racks or fault domains, where N is the number of hosts in each fault domain.