DR - Disaster Recovery

Enhanced Definition

Disaster Recovery (DR) in the mainframe context refers to the comprehensive process and set of procedures designed to restore critical z/OS systems, applications, and data following a catastrophic event that renders the primary data center or its core infrastructure inoperable. Its primary purpose is to ensure business continuity, minimize downtime, and protect data integrity by enabling operations to resume at an alternate recovery site. Disaster Recovery (DR) refers to the comprehensive set of policies, tools, and procedures designed to enable the rapid recovery or continuation of vital technology infrastructure and systems following a catastrophic event. In the mainframe and z/OS context, its primary purpose is to ensure business continuity for mission-critical applications and data, minimizing downtime and data loss after a natural disaster, major outage, or cyberattack affecting the primary data center.

Key Characteristics

- High Availability Integration: Often an extension of a high availability strategy, focusing on recovery from widespread outages rather than localized component failures.
- Data Replication Technologies: Leverages advanced data replication solutions like PPRC (Peer-to-Peer Remote Copy), XRC (Extended Remote Copy), and GDPS (Geographically Dispersed Parallel Sysplex) to maintain synchronized data at a remote recovery site.
- Recovery Time Objective (RTO) & Recovery Point Objective (RPO): Defined metrics that dictate the maximum acceptable downtime and data loss, respectively, which are critical for designing and validating mainframe DR solutions.
- Rigorous Testing: Requires frequent, full-scale DR tests to validate the recovery plan, procedures, and the readiness of the recovery site, given the complexity and criticality of mainframe workloads.
- Geographic Separation: Recovery sites are typically located a significant distance from the primary site to protect against regional disasters affecting both locations.
- Automated Failover/Failback: Advanced solutions like GDPS provide automated or semi-automated failover capabilities to the recovery site and subsequent failback to the primary site once it's restored.

Use Cases

- Regional Data Center Outage: Recovering mainframe operations after a natural disaster (e.g., flood, earthquake, hurricane) or widespread power grid failure renders the primary data center inaccessible.
- Catastrophic Hardware Failure: Restoring systems and data following an unrecoverable failure of core mainframe hardware components (e.g., an entire CPC or DASD subsystem) at the primary site.
- Major Software Corruption/Cyberattack: Recovering from widespread data corruption, operating system failures, or a sophisticated cyberattack (e.g., ransomware) by activating a clean copy of systems and data at the recovery site.
- Regulatory Compliance: Meeting stringent industry regulations (e.g., financial services, healthcare) that mandate robust business continuity and disaster recovery capabilities for critical IT infrastructure.
- Planned Site Migration: While not a disaster, DR capabilities can be leveraged for complex, large-scale planned data center migrations to minimize downtime and risk.

Related Concepts

DR is a critical component of a broader Business Continuity Plan (BCP), specifically addressing the IT infrastructure aspect. It relies heavily on Data Replication technologies (like PPRC, XRC, GDPS) to ensure that data at the recovery site is current and consistent. It is also closely related to High Availability (HA), as HA strategies aim to prevent outages, while DR focuses on recovering from them when they occur. Robust Backup and Recovery procedures are foundational for DR, providing the means to restore systems and data, especially for less critical applications or as a last resort.

Best Practices:

Define and Document RTO/RPO: Clearly establish and regularly review RTO and RPO targets for all critical applications, aligning them with business requirements and regulatory mandates.
Conduct Regular, Full -Scale Testing: Perform comprehensive DR tests at least annually, involving all relevant teams and validating the entire recovery process, including application startup and data integrity.
Automate Where Possible: Implement automated failover and failback solutions (e.g., GDPS) to reduce human error, accelerate recovery, and improve RTO.
Maintain Current Documentation: Keep DR plans, runbooks, contact lists, and configuration details meticulously updated to reflect any changes in the primary or recovery environments.
Ensure Geographic Separation: Design recovery sites with sufficient physical distance from primary sites to mitigate the risk of a single regional disaster impacting both locations.
Secure the Recovery Site: Apply the same rigorous security controls and access management to the DR site and its data as are applied to the primary production environment.