Re: Set copy as production vs Failback to production
Once you failover with a multi-copy CG you have both of these options available to you. Failback will reinstate the replication to all replica copies from the original Production copy.
Set Production confrms the failover replica copy as the new Production and initiates replication to additional replicas other than the original Production copy which is already receiving writes after the failover. Therefore the target replica which will become Production (source) for all replicas.