IASID - Internal ASID

Enhanced Definition

An IASID (Internal Address Space ID) is a specific type of ASID (Address Space ID) used by the z/OS operating system itself to identify and manage its internal, critical components and system-level functions. Unlike regular ASIDs assigned to user jobs, started tasks, or TSO users, IASIDs are reserved for core system services.

Key Characteristics

- System-Owned: IASIDs are exclusively assigned and managed by the z/OS operating system for its own use, not for user applications.
- Critical Functions: They host essential system services such as the System Resource Manager (SRM), System Logger, RMF, and other core components vital for system operation.
- Non-Swappable: Address spaces identified by IASIDs are typically resident in real storage and are not eligible for swapping, ensuring their continuous availability and performance.
- High Privilege: Components running under an IASID operate with high system authority and access privileges necessary to manage system-wide resources.
- Stability and Integrity: IASIDs are fundamental to maintaining the overall stability, integrity, and security of the z/OS environment.
- Reserved Range: While not strictly fixed, IASIDs are often allocated from a specific, typically higher-numbered range of available ASIDs.

Use Cases

- System Resource Manager (SRM): The SRM itself runs in an internal ASID, managing system resources like CPU, memory, and I/O.
- System Logger: The component responsible for managing log streams for various system and application logging facilities operates under an IASID.
- Resource Measurement Facility (RMF): RMF gatherers and post-processors, which collect and analyze system performance data, utilize internal ASIDs.
- Global Resource Serialization (GRS): The GRS complex, which manages access to shared resources across multiple z/OS systems, runs in an IASID.
- Cross-Memory Services: Facilitating communication and data transfer between different address spaces, including system-level services.

Related Concepts

An IASID is a specialized instance of an ASID (Address Space ID), which uniquely identifies an address space within a z/OS system. While regular ASIDs are for user workloads, IASIDs are for the operating system's own critical functions, making them integral to system integrity and the proper functioning of the SRM (System Resource Manager) which manages all address spaces. They are distinct from TSO or batch job ASIDs.

Best Practices:

System Monitoring: Regularly monitor the health and resource consumption of system-owned address spaces (identified by IASIDs) to detect potential system bottlenecks or issues.
Avoid Interference: Never attempt to terminate, modify, or otherwise interfere with an address space identified by an IASID, as this can lead to severe system instability or a system crash.
Capacity Planning: When planning for total ASID capacity, account for the number of IASIDs required by the operating system, which can vary slightly with z/OS version and installed features.
Troubleshooting: In performance analysis or problem determination, be aware that high resource utilization by an internal ASID might indicate a system-level problem or a misbehaving component that is impacting core services.