Drive - Storage device
In the context of IBM mainframes and z/OS, a "drive" refers to a physical or virtual hardware component used for persistent data storage. This primarily encompasses **Direct Access Storage Devices (DASD)**, which are disk drives providing random access, and **magnetic tape drives**, which offer sequential access storage. These devices are fundamental for housing the operating system, application data, and backups.
Key Characteristics
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- DASD (Disk Drives): Provide high-speed, random access to data, organized into logical units like volumes, cylinders, tracks, and blocks. Modern DASD are typically enterprise-grade storage arrays (e.g., IBM DS8000 series) connected via FICON or Fibre Channel Protocol (FCP).
- Tape Drives: Offer high-capacity, cost-effective sequential access storage, primarily used for backups, archives, and data transfer. They utilize magnetic tape cartridges and can be physical drives or Virtual Tape Libraries (VTLs).
- Persistent Storage: Data stored on drives remains intact even after power cycles, ensuring data availability across system reboots.
- Device Numbers: Each physical or logical drive is assigned a unique hexadecimal device number (e.g.,
X'0A80') by z/OS for identification and I/O addressing. - Managed by z/OS: The operating system manages all I/O operations, space allocation, data integrity, and access control for data residing on these drives.
- Shared Access: DASD volumes can be shared across multiple z/OS systems within a sysplex environment, enabling data sharing and high availability.
Use Cases
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- Operating System Volumes: DASD drives host the z/OS operating system, its libraries (SYSRES), paging datasets, and system work areas.
- Application Data Storage: Storing various types of application data sets, including VSAM files, sequential files, PDS/PDSE libraries, and database files for DB2, IMS, and CICS.
- Backup and Archiving: Magnetic tape drives are extensively used for creating full system backups, application data backups, and long-term data archiving for compliance or historical purposes.
- Temporary Work Areas: Providing high-speed temporary storage for sorts, intermediate processing files, and other transient data required by batch jobs or online transactions.
- Database Storage: Dedicated DASD volumes are critical for housing the extensive data and log files for enterprise databases like IBM DB2 for z/OS and IMS DB.
Related Concepts
Drives are the physical foundation upon which data sets (logical files) are stored. JCL (Job Control Language) uses DD (Data Definition) statements to specify the data sets and, implicitly or explicitly, the volumes and drives where they reside. The Storage Management Subsystem (SMS) automates the allocation and management of data sets across different types of drives based on defined storage policies. All I/O operations performed by z/OS and applications ultimately interact with these underlying storage drives to read or write data.
- Implement SMS: Utilize Storage Management Subsystem (SMS) to automate data set placement, migration, backup, and recovery, ensuring optimal use of storage resources and adherence to service level agreements.
- Monitor I/O Performance: Regularly monitor DASD I/O metrics (e.g., response time, queue depth, channel utilization) to identify and resolve performance bottlenecks, ensuring efficient application execution.
- Utilize RAID and Replication: Employ RAID (Redundant Array of Independent Disks) configurations and storage replication technologies (e.g., IBM GDPS) for DASD to ensure data redundancy, high availability, and disaster recovery capabilities.
- Regular Backup and Recovery Testing: For tape-based backups, regularly test the recovery process to validate the integrity of the backups and the effectiveness of the recovery procedures.
- Leverage Virtual Tape Libraries (VTLs): Implement VTLs to improve tape backup and restore performance, reduce physical tape handling, and enhance automation and reliability compared to physical tape drives.