On each host that you want to add to a vSphere HA cluster, you must configure two different networking switches so that the host can also support vSphere Fault Tolerance.
To enable Fault Tolerance for a host, you must complete this procedure twice, once for each port group option to ensure that sufficient bandwidth is available for Fault Tolerance logging. Select one option, finish this procedure, and repeat the procedure a second time, selecting the other port group option.
Multiple gigabit Network Interface Cards (NICs) are required. For each host supporting Fault Tolerance, you need a minimum of two physical gigabit NICs. For example, you need one dedicated to Fault Tolerance logging and one dedicated to vMotion. Use three or more NICs to ensure availability.
After you create both a vMotion and Fault Tolerance logging virtual switch, you can create other virtual switches, as needed. Add the host to the cluster and complete any steps needed to turn on Fault Tolerance.
If you configure networking to support FT but subsequently disable the Fault Tolerance logging port, pairs of fault tolerant virtual machines that are powered on remain powered on. If a failover situation occurs, when the Primary VM is replaced by its Secondary VM a new Secondary VM is not started, causing the new Primary VM to run in a Not Protected state.