The CA Vtape Cache Monitor is a set of subtasks running in the SVTS or primary address space. These subtasks monitor DASD space or cache occupied by Virtual Volumes queued for Externalization, free-able DASD space occupied by Virtual Volumes previously Externalized, and available DASD space within the DASD buffer.
When Dynamic Cache Management is active, the subtasks invoke the DFSMS ACS routines to determine the storage groups assigned to the dynamic cache storage class. The storage groups returned by DFSMS are then processed using IDCAMS DCOLLECT to determine the available DASD space.
These subtasks determine when the automated Externalization or stacking subgroup queues should be released or held and when Virtual Volumes should be deleted from the cache.
In a CA Vtape Complex where multiple subsystems are sharing the same DASD buffer, a flag is set in the control data set to inform all the subsystems in the complex when one subsystem is doing space management. This prevents multiple subsystems from performing space management at the same time on the shared DASD buffer.
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