Coupling facility storage considerations for duplexing

When planning for storage, make the primary and secondary group buffer pool structures the same size.

If your system is properly configured for high availability using a simplexed group buffer pool, you usually do not need extra coupling facility storage for duplexing. For simplexed structures, you must reserve enough spare capacity in the coupling facilities to be able to absorb the structures of any failed coupling facility. With duplexed structures, instead of reserving storage in case of a coupling facility failure, that storage is used by the secondary group buffer pool.

For example, assume that you have 2 coupling facilities, each with 1 GB of memory, for a total of 2 GB of memory. Ensure that the total size of the structures across the 2 coupling facilities does not exceed 1 GB (50% of the total coupling facility storage).

If you configure three or more coupling facilities, you might need an additional coupling facility for duplexing.