Planning the GRS system parameter

The GRS system parameter indicates whether the system is to join a global resource serialization complex.

In a multisystem sysplex, every system in the sysplex must be in the same global resource serialization complex. This allows global serialization of resources in the sysplex.

To initialize each MVS™ system in the multisystem sysplex, you must use the global resource serialization component of MVS. You can use another product to serialize the use of shared resources, but global resource serialization is also required.

System Logger has special requirements for multiple sysplexes in a GRS Ring Complex environment. See Sysplex requirement.

For a global resource serialization star complex, specify

GRS=STAR

The effect that STAR has depends on the system configuration as follows:

XCF-local mode (PLEXCFG=XCFLOCAL): This configuration is not allowed in a star complex. Message ISG303D is issued, and the operator is prompted to either re-IPL the system or to continue the IPL with GRS=NONE.
Single-system sysplex (PLEXCFG=MONOPLEX): This configuration is not allowed in a star complex. Message ISG303D is issued, and the operator is prompted to either re-IPL the system or to continue the IPL with GRS=NONE.
Default sysplex configuration (PLEXCFG=ANY): If XCF is in local mode, this configuration is not allowed. Otherwise, the system is initialized into a global resource serialization star complex and XCF protocols are used in the complex.
Multisystem sysplex (PLEXCFG=MULTISYSTEM): The system starts or joins an existing sysplex and a global resource serialization star complex. XCF coupling services are used in the sysplex and in the complex.

For a global resource serialization ring complex, specify one of the following:

GRS=JOIN or START or TRYJOIN

The effect of JOIN, START, or TRYJOIN depends on the sysplex configuration, as follows:

XCF-local mode (PLEXCFG=XCFLOCAL): There is only one system (in XCF-local mode) in the sysplex. The system starts or joins an existing global resource serialization complex and non-XCF protocols are used in the complex.
Single-system sysplex (PLEXCFG=MONOPLEX): There is only one system in the sysplex. The system starts or joins an existing global resource serialization complex and non-XCF protocols are used in the complex.
Multisystem sysplex (PLEXCFG=MULTISYSTEM): The system starts or joins an existing sysplex and a global resource serialization complex. XCF coupling services are used in the sysplex and the complex. (For systems in the complex that are not in the sysplex, non-XCF protocols are used.)

GRS=NONE

The effect of NONE depends on the intended sysplex configuration, as follows:

XCF-local mode (PLEXCFG=XCFLOCAL): There is only one system (in XCF-local mode) in the sysplex and no global resource serialization complex.
Single-system sysplex (PLEXCFG=MONOPLEX): There is only one system in the sysplex and no global resource serialization complex.
Multisystem sysplex (PLEXCFG=MULTISYSTEM): This is not allowed. Global resource serialization is required in a multisystem sysplex.