DASDM - DASD Management

Enhanced Definition

DASD Management (Direct Access Storage Device Management) refers to the comprehensive set of processes, tools, and policies used to administer, optimize, and maintain the storage resources provided by DASD on IBM z/OS mainframe systems. Its primary purpose is to ensure efficient space utilization, high performance, data availability, and integrity for all datasets and databases residing on these storage devices.

Key Characteristics

- Space Allocation and Deallocation: Manages how datasets acquire space on DASD volumes, including primary, secondary, and extended space allocations, and how that space is released when datasets are deleted.
- Performance Optimization: Involves strategies like proper dataset placement, I/O path optimization, and workload balancing to minimize access times and maximize throughput.
- Availability and Recovery: Implements backup, recovery, and replication strategies (e.g., using DFSMSdss, DFSMShsm, GDPS) to ensure data is always accessible and can be restored in case of failures.
- Capacity Planning: Monitors current storage usage, analyzes growth trends, and forecasts future storage requirements to prevent outages and ensure sufficient resources.
- Data Integrity and Security: Employs mechanisms to protect data from corruption, unauthorized access, and loss, often integrating with security systems like RACF.
- Automation via SMS: Leverages the Storage Management Subsystem (SMS) to automate policy-based management of datasets, including allocation, migration, backup, and retention.

Use Cases

- New Application Deployment: Allocating and configuring appropriate DASD space and performance characteristics for new application datasets, VSAM files, DB2 table spaces, or IMS databases.
- Performance Tuning: Reorganizing frequently accessed datasets, moving them to faster storage tiers (e.g., SSDs), or adjusting block sizes to improve application response times.
- Disaster Recovery Planning: Implementing and testing remote replication technologies and backup procedures to ensure business continuity in the event of a site-wide disaster.
- Storage Migration and Consolidation: Moving data from older, less efficient DASD arrays to newer, higher-capacity, or more performant storage solutions without application disruption.
- Auditing and Reporting: Generating reports on DASD utilization, free space, dataset growth, and I/O statistics to aid in chargeback, compliance, and resource planning.

Related Concepts

DASD Management is foundational to nearly all z/OS operations. It works closely with JCL (Job Control Language), where DD statements specify dataset characteristics and allocation parameters. The Storage Management Subsystem (SMS), a key component of DFSMS (Data Facility Storage Management Subsystem), is the primary tool for automating DASD management policies. Catalogs (VSAM/ICF) rely on DASDM to manage the physical location of datasets, while database systems like DB2 and IMS depend heavily on efficient DASD management for their data, index, and log files.

Best Practices:

Implement DFSMS and SMS: Fully leverage DFSMS and SMS to automate storage management, enforce policies, and improve efficiency by reducing manual intervention.
Proactive Capacity Planning: Regularly monitor DASD usage and growth, and proactively plan for future requirements to avoid "out of space" conditions and ensure continuous operations.
Data Tiering: Implement data tiering strategies, placing critical, frequently accessed data on high-performance storage (e.g., flash/SSD) and less critical or archival data on more cost-effective tiers.
Robust Backup and Recovery: Establish and regularly test comprehensive backup and recovery procedures, including offsite storage and disaster recovery drills, to ensure data resilience.
Standardized Naming Conventions: Enforce consistent and meaningful dataset naming conventions to simplify identification, management, and automation.
Regular Maintenance: Perform routine maintenance tasks such as dataset reorganization, space reclamation, and volume defragmentation to maintain optimal performance and space utilization.