GRSCNF

Enhanced Definition

`GRSCNF` (Global Resource Serialization Configuration) is a member within `SYS1.PARMLIB` that defines the configuration for Global Resource Serialization (GRS) on a z/OS system. It specifies parameters that control how GRS manages global resources across a sysplex, ensuring data integrity and preventing deadlocks by serializing access to shared resources. This configuration is crucial for systems participating in a GRS complex, whether in a ring or star configuration.

Key Characteristics

- Location: Resides in SYS1.PARMLIB and is typically named GRSCNFxx, where xx is a two-character suffix. The specific member loaded at IPL is determined by the GRSCNF parameter in IEASYSxx.
- Purpose: Defines the GRS operational mode (RING or STAR), identifies the systems participating in the GRS complex, and specifies parameters for GRS communication and resource management.
- Contents: Contains statements like GRSMODE (specifying RING or STAR), SYSTEMS (for RING mode), PLEXCFG (for STAR mode, defining Coupling Facility structures), and other optional parameters that fine-tune GRS behavior.
- Dynamic Updates: While some GRSCNF parameters require an IPL to take effect, others can be dynamically updated using the SET GRSCNF operator command, allowing for configuration changes without system downtime.
- Sysplex-Wide Impact: Changes to GRSCNF affect the entire GRS complex, influencing how global ENQs (enqueue requests) are managed and resolved across all participating z/OS systems, impacting shared resource access.
- Coupling Facility Dependency: In STAR GRS mode, GRSCNF specifies the Coupling Facility (CF) structures used by GRS for global resource serialization, making it dependent on CF availability, connectivity, and configuration for its operation.

Use Cases

- Initial GRS Setup: Defining the initial GRS configuration when bringing up a new z/OS sysplex or adding a system to an existing GRS complex, specifying whether it will operate in RING or STAR mode.
- Migrating GRS Mode: Changing the GRS operational mode for a sysplex, for example, migrating from a less scalable RING GRS configuration to a more robust and performant STAR GRS configuration.
- Adding/Removing Systems: Updating the GRSCNF to include new z/OS systems joining the GRS complex or to remove systems that are no longer participating in global resource serialization.
- Performance Tuning: Adjusting GRS parameters, such as the RESERVE conversion options or GRSDEF parameters (if specified within GRSCNF or pointed to by it), to optimize global ENQ processing and reduce contention.
- Disaster Recovery Planning: Ensuring GRSCNF is correctly configured for disaster recovery scenarios, especially in a STAR GRS setup where CF structures might need to be