In the event of a catastrophic outage, you can quickly restore any affected system by “failing over” to a copied version.
failover is the transfer of business-critical workloads away from a compromised primary production system and to a designated recovery site— thereby restoring production system operations. Failover mitigates the effects of a disruption by sustaining operations in the face of a potentially debilitating system failure.
Failback
Failback allows you to recover the pre-disaster image at the original production system (or other selected production location) and restore workloads from the copied system to the designated production system.
Thus, you must synchronize the restored/new production system with the copied system prior to failback in order to avoid business-critical information loss.
When executing a failback, only the interim (altered) data retained in the recovery system should be returned to the new/restored production system.