Backup

Enhanced Definition

A backup in the mainframe context is a copy of data (such as datasets, volumes, or database objects) created at a specific point in time, primarily for disaster recovery, data restoration, or historical archiving. Its main purpose is to ensure business continuity and data integrity by enabling recovery from data loss, corruption, or system failures.

Key Characteristics

- Granularity: Backups can range from full DASD volume images (e.g., DFSMShsm DUMPs) to individual sequential datasets, VSAM files, DB2 table spaces, or IMS databases.
- Methods and Utilities: Utilizes specialized z/OS utilities like ADRDSSU (Data Set Services Utility), DFSMSdss (Data Set Services), DFSMShsm (Hierarchical Storage Manager), DB2 utilities (COPY), and IMS utilities (IMAGE COPY).
- Storage Media: Backups are typically stored on magnetic tape (physical or virtual VTL), DASD (for faster recovery), or increasingly, off-platform cloud storage via z/OS connectors.
- Point-in-Time Recovery: Backups capture data as it existed at the moment the backup was taken, enabling restoration to that exact state.
- Consistency: For transactional systems like DB2 and IMS, backups must be logically consistent, often achieved by quiescing activity or using specialized database utilities that ensure data integrity.
- Automation: Often integrated into automated batch jobs, JCL procedures, or DFSMShsm policies for scheduled, routine execution.

Use Cases

- Disaster Recovery: Restoring entire z/OS systems, critical applications, or databases after a major outage at a primary data center.
- Data Corruption or Loss: Recovering specific datasets, VSAM files, or database objects that have been accidentally deleted, overwritten, or corrupted.
- System Migration/Upgrade: Creating a baseline copy of data before major system changes, allowing for rollback if issues arise.
- Auditing and Compliance: Retaining historical copies of data for regulatory compliance, legal discovery, or long-term archiving requirements.
- Application Testing: Providing a consistent copy of production data for use in development or test environments, often after anonymization or masking.

Related Concepts

Backups are fundamental to Data Recovery and Business Continuity Planning (BCP) on the mainframe. They are often managed by DFSMShsm for automated scheduling and migration, and rely on JCL for execution of utilities like ADRDSSU or DFSMSdss. For databases, DB2 and IMS provide their own specialized backup utilities that integrate with DBRC (Database Recovery Control) to ensure data integrity and track recovery assets.

Best Practices:

Regular Scheduling: Implement automated, regularly scheduled backups (daily, weekly, monthly) based on data criticality and change frequency using JCL or DFSMShsm policies.
Verification and Testing: Periodically test the restorability of backups to ensure data integrity and validate recovery procedures, including full system recovery drills.
Offsite Storage: Store critical backups offsite to protect against site-wide disasters, often using tape libraries or secure cloud solutions.
Retention Policies: Define and enforce clear retention policies for different types of backups (e.g., daily, weekly, monthly, yearly) to meet compliance and recovery objectives.
Database Consistency: For DB2 and IMS, always use database-specific utilities (COPY for DB2, IMAGE COPY for IMS) to ensure transactional consistency and integrate with DBRC for robust recovery.