Data Facility

Enhanced Definition

Data Facility refers to a suite of IBM software products within the z/OS environment designed to manage, store, protect, and optimize access to data. These facilities provide comprehensive services for data set management, storage management, data migration, backup, recovery, and tape library management, ensuring efficient and reliable data handling for mainframe applications.

Key Characteristics

- Integrated Storage Management: The primary component, DFSMS (Data Facility Storage Management Subsystem), provides policy-based, automated management of storage resources, including DASD (Direct Access Storage Devices) and tape.
- Hierarchical Storage Management: DFSMShsm (Hierarchical Storage Manager) automates the migration of data between different storage tiers (e.g., primary, migration, backup) based on usage patterns and policies, optimizing storage costs and performance.
- Data Set Services: Manages various data set organizations like sequential data sets, PDS (Partitioned Data Sets), PDSE (Partitioned Data Set Extended), and VSAM (Virtual Storage Access Method) data sets.
- Backup and Recovery: DFSMSdss (Data Set Services) provides high-speed data movement, backup, and recovery capabilities for entire volumes or individual data sets.
- Tape Library Management: DFSMSrmm (Removable Media Manager) manages physical and virtual tape libraries, tracking tape volumes, their contents, and their locations to prevent accidental overwrites and simplify retrieval.
- Policy-Driven Automation: Data Facility components leverage SMS (Storage Management Subsystem) policies to automate decisions regarding data placement, retention, backup, and migration, reducing manual intervention.

Use Cases

- Automated Data Tiering: Automatically migrating infrequently accessed data from expensive, high-performance DASD to cheaper, slower storage tiers (e.g., tape or lower-cost disk) using DFSMShsm.
- Disaster Recovery Planning: Performing full volume or data set backups using DFSMSdss, often to remote sites, as a critical part of a disaster recovery strategy.
- Efficient Data Set Allocation: Using SMS policies to automatically assign new data sets to appropriate storage groups, ensuring they meet performance, availability, and cost requirements without manual specification in JCL.
- Tape Volume Management: Tracking the lifecycle of tape cartridges, managing their expiration, and ensuring data integrity for archival purposes using DFSMSrmm.
- Space Management: Reclaiming unused space on DASD volumes and managing fragmented space to optimize storage utilization.

Related Concepts

Data Facility software is fundamental to z/OS, acting as the operating system's primary mechanism for managing storage and data. It interacts closely with JCL by interpreting data set allocation requests and applying SMS policies. Applications written in COBOL, PL/I, or Assembler rely on the Data Facility to access and manage their data sets, whether they are VSAM files, sequential files, or PDS members. It also integrates with DB2 and IMS to manage the underlying data sets that these database systems use.

Best Practices:

Define Comprehensive SMS Policies: Develop robust SMS policies that accurately reflect business requirements for data availability, performance, and retention, ensuring optimal data placement and management.
Regularly Review and Tune Policies: Periodically review SMS constructs (Storage Groups, Management Classes, Data Classes) and policies to adapt to changing application needs, data growth, and hardware advancements.
Implement Robust Backup and Recovery Strategies: Utilize DFSMSdss and DFSMShsm effectively to establish a comprehensive backup and recovery plan, including regular testing of recovery procedures.
Monitor Storage Utilization: Proactively monitor DASD and tape utilization, free space, and performance metrics to identify potential bottlenecks or capacity issues before they impact operations.
Leverage DFSMShsm for Archiving: Use DFSMShsm for automated archiving and recall of historical or infrequently accessed data to reduce primary storage costs and improve performance for active data.