Designing a star complex

The star method for processing requests for global resources operates in a sysplex like any other MVS™ component that uses the coupling facility. Unlike the ring method, which might require you to set up XCF signalling paths for the SYSGRS group, the star method will operate well without any special definitions. There is no need to set up XCF signalling paths between systems or to define CTC links directly to global resource serialization.

Figure 1. The Star Concept

XCF requires a DASD data set, called a sysplex couple data set, to be shared by all systems. An alternate data set can be used to facilitate migrating from a ring to a star complex. On the sysplex couple data set, MVS stores information related to the sysplex, systems, and XCF groups, such as global resource serialization.

The following policies are used to manage global resource serialization:

Coupling facility resource management (CFRM) policy, which is required, defines how MVS manages coupling facility resources.
Sysplex failure management (SFM) policy, which is optional, defines how MVS is to manage sysplex resources. GRS exploits both XCF and XES critical member support and indicates a TERMLEVEL of SYSTEM. For more information about defining SFM policy, see z/OS MVS Setting Up a Sysplex. IBM® suggests using the SFM policy.