Why we need to disable HA for Enabling the VSAN in Cluster?

Q. Why "When enabling VSAN ensure vSphere HA is disabled. You cannot enable VSAN when HA is already configured. Either configure VSAN during the creation of the cluster or disable vSphere HA temporarily when configuring VSAN."?

Ans. Reason behind this is when VSAN is enabled with HA then HA is not using Management Network for the Heartbeat Traffic it uses "VSAN Network" for the Heartbeat Traffic. For making these fundamental changes in the architecture HA needs to disabled before enabling the VSAN in the Cluster.

Error Message if you will try to enable VSAN on the Cluster where HA is already Enabled

 
Note:-
Be aware that when HA is turned on in the cluster, FDM agent (HA) traffic goes over the VSAN network and not the Management Network. However, when an potential isolation is detected HA will ping the default gateway (or specified isolation address) using the Management Network.