GFS - Grandfather Father Son
GFS (Grandfather Father Son) is a widely used data retention and backup strategy in mainframe environments, particularly for sequential datasets like those on magnetic tape or disk. It involves maintaining multiple generations of a dataset, typically three: the most recent (Son), the previous (Father), and the one before that (Grandfather). This strategy provides a balanced approach to data recovery capabilities and storage efficiency.
Key Characteristics
-
- Generational Approach: Data is saved in distinct "generations" or versions, allowing for rollback to previous states if corruption or error occurs.
- Cyclical Rotation: As a new "Son" generation is created, the current "Son" becomes the "Father," the "Father" becomes the "Grandfather," and the oldest "Grandfather" is typically retired, uncataloged, or reused.
- Sequential Data Focus: Primarily applied to sequential datasets, often stored on magnetic tape or disk, making it ideal for batch processing outputs.
- Recovery Point Objective (RPO): The number of generations directly impacts the RPO, determining how far back in time data can be recovered.
- Simplicity and Efficiency: It's a relatively straightforward and effective strategy for managing backups of frequently updated data, especially when integrated with tape libraries.
- JCL and GDG Integration: Often implemented and managed in z/OS using Generation Data Groups (GDGs), which automate the cataloging and management of these generational files via JCL.
Use Cases
-
- Daily Batch Processing: Backing up critical transaction files, master files, or intermediate work files that are updated daily by batch jobs.
- Database Backups: Storing sequential copies of database unload files (e.g., DB2 image copies, IMS log files) before applying updates or for recovery purposes.
- Reporting and Archiving: Maintaining historical versions of large report files, audit trails, or output from critical applications for compliance or analytical needs.
- Disaster Recovery Planning: Providing multiple recovery points for restoring critical application data in the event of data corruption, system failure, or accidental deletion.
Related Concepts
GFS is fundamentally linked to Generation Data Groups (GDGs) in z/OS, which provide the system-level mechanism to define, manage, and catalog these generational datasets automatically. It is a core strategy for data backup and recovery within the mainframe ecosystem and is typically implemented via JCL using DD statements that reference GDG base entries. It complements broader data management and disaster recovery plans by offering a structured, automated approach to data versioning for sequential files.
- Automate with GDGs: Always leverage z/OS Generation Data Groups (GDGs) to automate the creation, cataloging, and management of GFS generations, ensuring consistency and reducing manual errors.
- Define Clear Retention Policies: Establish and document the number of generations to keep (e.g., 3 for traditional GFS, but can be extended) and their retention periods to meet specific recovery objectives and regulatory compliance requirements.
- Offsite Storage for Critical Data: For highly critical data, ensure that at least one older generation (e.g., the Grandfather) is moved to secure offsite storage for robust disaster recovery capabilities.
- Regular Recovery Testing: Periodically test the data recovery process using GFS generations to validate data integrity, ensure the effectiveness of the backup strategy, and verify recovery procedures.
- Monitor Storage Usage: Regularly monitor the disk or tape space consumed by GFS generations, especially when using disk-based GDGs, to prevent storage exhaustion and optimize resource utilization.