Failback - Returning to primary

Enhanced Definition

Failback is the process of returning IT operations, applications, and data processing to the original, primary system or site after a failover event. This action typically occurs once the primary system has been repaired, restored, and thoroughly verified to be stable and ready for production workload. It is the reverse operation of a failover.

Key Characteristics

- Reversal of Failover: It is the planned and controlled transition back to the primary system or data center after a period of running on a secondary (backup) system following a failover.
- Data Synchronization: Requires meticulous synchronization of all data changes that occurred on the secondary system back to the primary system to ensure data consistency and integrity.
- Planned Operation: Unlike an unplanned failover, failback is almost always a planned event, often requiring a scheduled outage or maintenance window for the affected applications.
- System Verification: Involves comprehensive testing and verification of the primary system's health, performance, and readiness before the workload is shifted back.
- Minimizes Disruption: A well-executed failback aims to minimize service disruption and data loss during the transition, ensuring a smooth return to normal operations.

Use Cases

- Post-Disaster Recovery: After a disaster event (e.g., primary data center outage) where operations were shifted to a recovery site, failback is used to return to the restored primary data center.
- Planned Maintenance: When a primary system or component undergoes planned maintenance (e.g., hardware upgrade, OS patch), workload might be temporarily failed over to a secondary system, then failed back once maintenance is complete.
- Hardware Failure Recovery: Following a critical hardware failure on the primary mainframe, failover to a backup system occurs; once the primary hardware is replaced and verified, failback restores normal operations.
- Testing and Drills: Failback procedures are routinely practiced during disaster recovery drills to ensure the organization's ability to restore normal operations efficiently.

Related Concepts

Failback is intrinsically linked to Failover, forming a complete business continuity cycle. While failover shifts operations to a backup, failback brings them back to the primary. It is a critical component of Disaster Recovery (DR) strategies, ensuring the ability to not only recover from an outage but also to return to the optimal primary operating environment. Effective failback relies heavily on robust Data Replication technologies (e.g., GDPS, XRC, PPRC) to ensure data consistency between sites. It also contributes to overall High Availability (HA) by allowing systems to return to their most resilient and often highest-performing configuration.

Best Practices:

Thorough Primary System Validation: Before initiating failback, rigorously test and validate the primary system's health, configuration, and application readiness.
Complete Data Reconciliation: Ensure all data updates and changes made on the secondary system are fully replicated and reconciled with the primary system to prevent data loss or inconsistencies.
Scheduled Maintenance Window: Plan the failback during a low-activity window to minimize impact on users and business operations, as it often requires a temporary application outage.
Detailed Runbook and Documentation: Maintain a comprehensive, up-to-date failback runbook with step-by-step procedures, contact information, and verification checklists.
Regular Testing and Drills: Incorporate failback scenarios into regular disaster recovery testing to identify potential issues and ensure personnel proficiency.
Post-Failback Monitoring: Closely monitor system performance, application functionality, and data integrity on the primary system immediately after failback to detect and resolve any anomalies quickly.