What are the benefits to have a fail over VMS server over a fail over NVR ? is raid 5,6 enough for data protection or we need redundancy?

Its good for data protection.

It protects all the data and the next server will end up taking over if previous server had failed.

Raid 5 in enough and other server is tak over 

Raid 5 is enough for the fail over and benefit is next server will take over the role if previous server or primary server fail