Enlargement

Increasing Size

Enhanced Definition

In z/OS, enlargement refers to the process of increasing the allocated storage capacity for a resource, primarily datasets or the virtual storage region available to a job or address space. Its primary purpose is to accommodate growing data volumes or provide sufficient memory for program execution, preventing out-of-space conditions or storage-related abends.

Key Characteristics

- Dataset Enlargement: Can involve increasing primary and/or secondary allocations for datasets (e.g., VSAM, sequential, PDS/PDSE). For some dataset types (like VSAM), it can occur dynamically, while others may require re-allocation or migration.
- Region Size Enlargement: Achieved by specifying a larger value in the REGION parameter in JCL, increasing the amount of virtual storage (below and above the 16MB line, and 2GB bar) available to a batch job or started task.
- Dynamic vs. Static: VSAM datasets can often be dynamically enlarged by the system as data is added, utilizing secondary allocations. Other dataset types might require explicit intervention (e.g., ALTER command for VSAM, re-defining for sequential).
- Limits and Constraints: Enlargement is subject to system limits (e.g., maximum dataset size, volume capacity, MEMLIMIT for 64-bit storage) and dataset organization rules.

Use Cases

- Expanding a VSAM KSDS: When a key-sequenced data set (KSDS) approaches its capacity, enlargement allows it to store more records without requiring a full unload/reload.
- Increasing a Sequential Dataset's Capacity: A sequential dataset used for logging or report generation may need to be enlarged to hold more output than initially planned.
- Providing More Memory for a Batch Job: A COBOL program processing a large in-memory table or a sort utility handling a massive input file might require a larger REGION to avoid S878 or S40D abends.