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Control File Blocks and the Global-Copy Process

The number of control file blocks in-use at any moment in time is very fluid. In a typical synchronized MIMplex, only one or two control file blocks are used from control file cycle to control file cycle. The largest usage of control file blocks occurs during MIMplex transition states. For example, when a new CA MIM address space is joining an existing MIMplex, or when a control file migration occurs. During these transition states, CA MIM generates a large volume of transactions to represent all outstanding resources at the moment the transition state began. This generation allows the newly joining system or re-synchronizing systems (in the case of a migration), to understand immediately the global resource environment at that moment in time.

The currently active system that detects the newly joining system (and has the current global picture of all managed resources) initiates a global-copy. The volume of transactions that are generated during a given global-copy operation depends the amount of managed resource activity at the time the global-copy was initiated. Once all global-copy transactions are placed in the control file, the newly joining CA MIM address space reads, processes, and removes them from the control file. At that point, the newly joining system is synchronized with the rest of the MIMplex. Once all global-copy transactions are removed from the control file, the MIMplex resumes to using only one or two control file blocks.

The CA MIM control file must be large enough to handle the volume of transactions that are generated as part of a global-copy operation. If the control file is too small, then CA MIM attempts to use an alternate control file. If all alternate control files are too small, then CA MIM ends abnormally with a U0095 RC=55. To avoid this ABEND, provide a control file large enough to handle global-copy operations should it be initiated during a period of peak activity. The maximum number of blocks that are used during a global-copy operation in your environment can be determined by examining the MAX USED field that is shown with the DISPLAY IO command. CA MIM also provides an early warning feature that provides an alert message when you exceed 50 percent of the total number of control file blocks.