IBM SC34-7012-01 manual Way Sysplex

However, using model log streams defined with the CICS default name are always assigned to the same structure within an MVS image. This may not give you the best allocation in terms of recovery considerations if you are using structures defined across two or more coupling facilities.

For example, consider a two-way sysplex that uses two coupling facilities, each with one log structure defined for use by CICS system logs, structures LOG_DFHLOG_001 and LOG_DFHLOG_002. In this situation, it is better from a recovery point of view for the CICS regions in each MVS to balance log stream allocations across both log structures. This scenario is illustrated in Figure 8, which shows a 2-way sysplex comprising MVSA and MVSB, with four CICS regions in each MVS. CICSA1 through CICSA4 reside in MVSA, and CICSB1 through CICSB4 reside in MVSB. Each MVS is using two coupling facilities, CF1 and CF2, each of which has one log structure referenced by model log streams. The first and second CICS regions in each MVS use log streams defined in the first log structure, and the third and fourth CICS regions in each MVS use log streams defined in the second log structure. In this scenario, each MVS image has a partner to recover its log streams in the event of an MVS failure.

	2-Way Sysplex
MVSA	CF1	MVSB
CICSA1	LOG_DFHLOG_001	CICSB1
CICSA2		CICSB2
	CF2
CICSA3	LOG_DFHLOG_002	CICSB3
CICSA4		CICSB4

Figure 8. Sharing system logger structures between 2 MVS images

Another example, shown in Figure 9 on page 112, is based on a 4-way sysplex comprising MVSA, MVSB, MVSC, and MVSD. In this case, ensure that the CICS regions that normally run on MVSA and MVSB use structure LOG_DFHLOG_001, and that the regions that run on MVSC and MVSD use structure LOG_DFHLOG_002. Thus each MVS image has a partner to recover its log streams in the event of an MVS failure. If a structure fails, the two MVS images using the other structure can take over the workload.

Chapter 11. Defining system and general log streams 111