If your installation is already running a ring, do the following to migrate to a star complex:

1. Set up new GRSCNFXX and IEASYSxx parmlib members to define the parameter information that will be needed later for the star complex. See z/OS MVS Initialization and Tuning Reference.
2. If the complex is a mixed complex, convert any non-sysplex systems to sysplex systems, or remove non-sysplex systems from the complex. Make sure that non-sysplex systems are not using resources that are shared by systems in the sysplex.
3. Do any hardware changes that need to be done to prepare for the use of the coupling facility hardware.
4. Define the ISGLOCK lock structure for global resource serialization. The structure must be accessible to all systems in the complex.
5. Create a new sysplex couple data set that contains the global resource serialization record, and make the new data set the active sysplex couple data set.
6. At this point, depending on what is best for your installation you can:
   • Take down the entire ring complex and re-IPL each system specifying GRS=STAR, or
   • Use the SETGRS MODE=STAR command to migrate from a ring to a star complex without a complex-wide IPL.