Geographically Dispersed

Enhanced Definition

In the context of IBM mainframe systems and z/OS, "geographically dispersed" refers to an architectural strategy where critical computing resources, data, and applications are distributed across multiple physically separate data centers located at significant distances from each other. The primary goal is to achieve extreme resilience, high availability, and robust disaster recovery capabilities by eliminating single points of failure associated with a single physical site or metropolitan area.

Key Characteristics

- Site Separation: Data centers are typically separated by hundreds or thousands of kilometers to mitigate the impact of regional disasters (e.g., natural disasters, widespread power outages).
- Data Replication: Employs advanced storage replication technologies (e.g., Metro Mirror, Global Mirror, z/OS Global Mirror) to maintain consistent data copies across all participating sites, often with near-real-time or asynchronous synchronization.
- Automated Recovery: Often leverages sophisticated automation software like GDPS (Geographically Dispersed Parallel Sysplex) to orchestrate automated failover and failback processes for z/OS images, Parallel Sysplex clusters, and storage subsystems.
- Redundant Infrastructure: Requires fully redundant hardware (processors, storage, network) and software at each dispersed site to ensure seamless operational continuity.
- Complex Management: Involves intricate planning, implementation, and ongoing management of network connectivity, data synchronization, and recovery procedures.
- High Cost: Represents a significant investment in infrastructure, software licenses, network bandwidth, and specialized personnel.

Use Cases

- Enterprise Disaster Recovery: Protecting mission-critical applications (e.g., banking transactions, airline reservations, government services) from catastrophic regional events.
- Business Continuity: Ensuring continuous operation and meeting stringent Recovery Time Objective (RTO) and Recovery Point Objective (RPO) requirements for essential business functions.
- Regulatory Compliance: Satisfying strict industry and governmental regulations that mandate high levels of data availability and rapid recovery capabilities.
- Global Operations Support: Providing highly resilient infrastructure for global enterprises that require 24/7 access to mainframe applications from various geographical locations.

Related Concepts

Geographically dispersed configurations are an evolution of high availability and disaster recovery strategies, extending the resilience offered by a Parallel Sysplex beyond a single data center or metropolitan area. While a Parallel Sysplex provides continuous availability within a local or metro-distance environment, geographically dispersed solutions, often orchestrated by GDPS, enable the entire sysplex or individual z/OS systems to survive a complete site failure by leveraging remote data replication and automated site switching. This approach directly addresses the limitations of Metroplex solutions which are vulnerable to widespread regional outages.

Best Practices:

Regular DR Testing: Conduct frequent, comprehensive disaster recovery drills that simulate real-world scenarios to validate recovery procedures, RTO/RPO targets, and staff proficiency.
Leverage Automation: Implement GDPS or similar automation tools to minimize manual intervention during failover and failback, reducing human error and accelerating recovery times.
Robust Data Synchronization: Continuously monitor and manage data replication mechanisms (Global Mirror, Metro Mirror) to ensure data integrity and consistency across all dispersed sites.
Diverse Network Paths: Design a highly resilient inter-site network infrastructure with multiple carriers and physically diverse routes to prevent network single points of failure.
Comprehensive Documentation: Maintain detailed and up-to-date documentation of all architectural components, operational procedures, and recovery plans, ensuring it is accessible at all sites.