Failback is the second stage of a two-part system for safeguarding information in a crisis mode during natural disasters or other events that can compromise an IT operation. Failback follows an initial stage called failover, in which data recording is switched to a new venue that will be safe from corruption or failure. In failback, specific data is saved to the original system to make up for any lapse.
Techopedia explains Failback
One of the implied characteristics of a failover and failback system is that the process is done automatically. At the time that an original system experiences a shut down or other jeopardy, the failover state begins, where new data is sent to the standby facility. When failover is done, failback begins. In a failback stage, the process uses something called change data, which represents changes made to the system under duress, or in other words, changes made only in the backup system.
In failback, only the change data is sent to the original system. This makes it easier to effectively back up the system, because everything that was already contained in it is salvaged. There is no need to copy an entire drive or set of drives; failback just adds what was recorded by the backup facility during the duration of the crisis. To accommodate failback (and failover) developers must create a remote mirror and other critical setup for this kind of event handling.
Failover and failback capability is valuable for systems that need to comply with various regulations in an industry. For example, systems can use failover and failback as part of a Health Insurance Portability and Accountability Act (HIPAA) Disaster Recovery Plan for compliance with HIPAA, an American law that addresses the safety of patient health data.