The star method of serializing global resources is built around a coupling facility in which the global resource serialization lock structure, ISGLOCK, resides. In a star complex, when an ISGENQ, ENQ, DEQ, or RESERVE macro is issued for a global resource, MVS™ uses information in the ISGLOCK structure to coordinate resource allocation across all systems in the sysplex.

Figure 1 shows the basic elements of a global resource serialization star complex. These elements include the systems, the coupling facility, and any shared resources (such as DASD) specified by the installation.

Figure 1. A Conceptual View of the Star Complex

In a star complex, global resource serialization requires the use of the coupling facility. The coupling facility makes data sharing possible by allowing data to be accessed throughout the sysplex by ensuring the data remain consistent among each system in the sysplex. The coupling facility provides the medium in global resource serialization to share information about requests for global resources between systems. Communication links are used to connect the coupling facility with the systems in the global resource serialization star sysplex. For more information on communication links, see z/OS MVS Setting Up a Sysplex.