The fourth system IPL

Figure 1 shows the multisystem environment after SYSD is initialized. The sysplex now matches the global resource serialization complex.

Figure 1. Four Systems in the Multisystem Sysplex

When SYSD is initialized and joins the sysplex, the sysplex matches the global resource serialization complex.

XCF coupling services are available on all systems, including signaling services between all systems.
The same primary sysplex couple data set is shared by all systems in the sysplex (not shown).
MVS™ component exploiters (such as global resource serialization) use signaling services between all systems.
Multisystem applications can use XCF coupling services and signaling services on all systems.
The systems must share a Sysplex Timer if they are running on separate CPCs (not shown).

Advantages: The following are some additional advantages when the multisystem sysplex matches the global resource serialization complex.
- The CTC links assigned in the GRSCNFxx parmlib member for the global resource serialization complex are no longer needed because global resource serialization uses signaling services to communicate between systems.
  See z/OS MVS Planning: Global Resource Serialization for the commands that you can use to vary the global resource serialization CTC links between SYSA and SYSB offline and then dynamically reassign them to XCF.
- There is reduced operator intervention when there is a ring disruption because global resource serialization can rebuild a global resource serialization ring without operator intervention.
- The resource name lists (RNLs) can be dynamically changed with the SET GRSRNL command while maintaining serialization integrity.