Coupling-facility size

The size of a coupling facility is defined as the total amount of storage it uses. Total storage includes both the control areas that the coupling-facility control code (CFCC) requires and data areas that applications use. The coupling-facility allocation rules and coupling-facility allocation-increment size, a function of the level of CFCC, affect the size of the coupling facility.

The storage in a coupling facility is divided into distinct objects called structures. The majority of coupling-facility storage is used for structures. The Coupling Facility Resource Management (CFRM) policy defines these structures.

To determine the size of the system logs, look at the individual batch jobs that you plan to use with DFSMStvs and estimate how much space they are likely to require. Determine how many batch jobs there are and how much data they are likely to update per transaction.

An estimate of the amount of storage that you need in a coupling facility for DFSMStvs should include an estimate of the space required for the primary and secondary system logs (undo log and shunt log) and the additional space required in the log of logs and forward recovery logs. The undo log and shunt log need to be large enough for backout logging from all the batch jobs that you plan to use with DFSMStvs, based on how much data that the jobs are likely to update for each transaction. You also need to make the log of logs and forward recovery logs large enough to account for the extra activity from the batch jobs; if these logs already exist, you need to increase their sizes. These logs might need to be twice as large if the batch activity would be roughly equivalent to CICS® activity and you do not plan to change your frequency of backups or of clearing out space in the forward recovery logs.