Introduction › GTAF › Device Integrity

Device Integrity

GTAF provides integrity for devices during the allocation process in two ways:

• By interfacing with the locking mechanism z/OS uses to locally serialize device allocation, GTAF prevents jobs on different systems from simultaneously allocating the same device.
• By communicating allocation information among systems, GTAF enables the local z/OS operating system to eliminate both locally and externally allocated devices when selecting a device for allocation. This prevents jobs from allocating devices that are already in use on another system.

z/OS provides device serialization on each system. GTAF then propagates that local serialization across all managed systems in the complex. As jobs on each system enter tape allocation, GTAF intercepts the request and forces the job to wait. GTAF then checks to verify that no job on any system is currently allocating from the same group of devices. When the requested device groups are free, the job is allowed to proceed through the normal allocation process.

Whenever a device is allocated or deallocated, GTAF writes a transaction representing the allocation or deallocation to the CA MIM control file. At regular intervals, GTAF on each system checks the control file for new information about device allocations and deallocations.

When GTAF reads a transaction about an allocation on another system, GTAF changes the local status of that device to “allocated.” This prevents jobs on the local system from allocating that device.