Continuity

Enhanced Definition

In the mainframe context, continuity refers to the ability of critical business applications, data, and IT services to operate without interruption, or to resume operations within defined service level agreements (SLAs) following a disruption. It encompasses strategies and technologies designed to minimize downtime, ensure data integrity, and maintain service availability in the face of failures, outages, or disasters.

Key Characteristics

- High Availability (HA): Utilizes redundant components and clustering technologies (like Parallel Sysplex) to eliminate single points of failure and automatically recover from component outages without human intervention.
- Disaster Recovery (DR): Involves establishing secondary, geographically separate sites and robust procedures to restore critical mainframe services and data in the event of a catastrophic primary site failure.
- Data Replication: Employs technologies such as PPRC (Peer-to-Peer Remote Copy), XRC (Extended Remote Copy), or Db2 Data Sharing to synchronize data between primary and recovery sites, minimizing data loss.
- Fault Tolerance: Design principles and system configurations that allow the system to continue operating correctly even when one or more components fail, often through redundancy and error detection/correction mechanisms.
- Recovery Time Objective (RTO): A defined metric specifying the maximum tolerable duration for restoring business operations after an outage or disaster.
- Recovery Point Objective (RPO): A defined metric specifying the maximum tolerable amount of data loss measured in time (e.g., 15 minutes of transactions) that can occur during a disaster.

Use Cases

- Critical Online Transaction Processing: Ensuring continuous availability of applications like CICS or IMS TM that handle millions of transactions daily, where even minutes of downtime can result in significant financial loss or customer dissatisfaction.
- Database Availability: Maintaining constant access to vital databases (e.g., DB2, IMS DB) through data sharing groups or replication, allowing applications to read and write data even if a database instance or LPAR fails.
- Batch Processing Resilience: Designing batch workflows to be restartable and recoverable, often leveraging checkpoint/restart mechanisms and robust job schedulers to resume processing efficiently after an interruption.
- Geographically Dispersed Operations: Implementing solutions like GDPS (Geographically Dispersed Parallel Sysplex) to provide continuous availability and disaster recovery across multiple data centers, often hundreds or thousands of miles apart.

Related Concepts

Continuity is intrinsically linked to High Availability (HA) and Disaster Recovery (DR), with HA focusing on preventing and quickly recovering from localized failures, and DR addressing site-wide catastrophes. It heavily relies on technologies like Parallel Sysplex for clustering and resource sharing, and GDPS for automated disaster recovery and workload balancing across geographically separated sites. Effective continuity planning integrates with Workload Manager (WLM) policies to prioritize critical applications during recovery and utilizes robust backup and recovery strategies for data integrity.

Best Practices:

Regularly Test Disaster Recovery Plans: Conduct periodic, full -scale DR drills to validate recovery procedures, identify gaps, and ensure RTO/RPO targets can be met under realistic conditions.
Implement Redundancy at All Levels: Design systems with redundant hardware (CPUs, I/O paths, power supplies), network connections, and software components to eliminate single points of failure.
Leverage z/OS High Availability Features: Utilize Parallel Sysplex for data sharing and workload balancing, Sysplex Distributor for network resilience, and Automatic Restart Manager (ARM) for automated application restarts.
Define and Monitor RTO/RPO: Clearly establish and document Recovery Time Objectives and Recovery Point Objectives for all critical applications and data, and continuously monitor system performance against these targets.
Automate Recovery Processes: Implement automation tools and scripts to streamline recovery procedures, reducing human error and accelerating the restoration of services during an