Esoteric Name - Symbolic device group name
An esoteric name in z/OS is a symbolic name assigned to a group of similar I/O devices, allowing a job step to request any available device from that group rather than a specific physical device. It provides device independence by abstracting the physical device selection, enhancing flexibility and resource utilization within the mainframe environment.
Key Characteristics
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- Device Abstraction: Hides the specific physical device address from the JCL, simplifying job definitions.
- Resource Pooling: Enables the operating system to select an available device from a defined pool of interchangeable resources (e.g., tape drives, DASD volumes).
- Dynamic Allocation: The z/OS operating system dynamically assigns an available device from the esoteric group at job execution time.
- IODF Definition: Esoteric names are defined and managed within the Input/Output Definition File (IODF), where they are associated with specific device types, control units, and physical devices.
- JCL Usage: Primarily used in the
UNIT=parameter of aDDstatement in JCL (e.g.,UNIT=TAPE,UNIT=SYSDA). - System-wide Scope: Once defined in the IODF and activated, an esoteric name is known and usable across the entire z/OS system.
Use Cases
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- Tape Drive Allocation: Requesting any available tape drive for backup, archive, or data transfer operations (e.g.,
UNIT=TAPEorUNIT=CART). - Temporary Disk Space: Allocating temporary disk space on any available direct access storage device (DASD) volume within a general-purpose pool (e.g.,
UNIT=SYSDAfor scratch datasets). - Generic Device Assignment: Ensuring job continuity by allowing the system to select an alternative device if a specific one is busy or offline, crucial for high availability.
- Printer Selection: Directing output to any available printer of a certain type, although often handled more granularly by JES output classes and device groups.
- Tape Drive Allocation: Requesting any available tape drive for backup, archive, or data transfer operations (e.g.,
Related Concepts
Esoteric names are a cornerstone of JCL (Job Control Language), specifically within the DD (Data Definition) statement's UNIT parameter, providing essential device independence. They are intrinsically linked to the IODF (Input/Output Definition File), which defines the hardware configuration and the mapping of esoteric names to physical devices and control units. This abstraction works in concert with dynamic allocation and MVS (Multiple Virtual Storage) resource management, allowing the operating system to efficiently manage and assign I/O resources to executing jobs and tasks.
- Meaningful Naming: Use clear, descriptive esoteric names that accurately reflect the device type or intended purpose (e.g.,
TAPE,SYSDA,ARCHIVE,WORKDSK). - IODF Management: Regularly review and update esoteric definitions in the IODF to reflect changes in hardware configuration, ensure optimal resource utilization, and remove obsolete entries.
- Standardization: Establish and enforce standard esoteric names across the z/OS environment to promote consistency in JCL, simplify system administration, and reduce errors.
- Avoid Over-generalization: While useful, avoid creating overly broad esoteric groups that might inadvertently assign an inappropriate device for a specific workload, potentially impacting performance or data integrity.
- Monitor Device Usage: Monitor the usage of devices within esoteric groups to identify bottlenecks, underutilized resources, or potential contention, allowing for adjustments to the IODF or workload distribution.