MVS cross-system MRO definitions

You can use CICS® interregion communication (IRC) for multiregion operation (MRO) between CICS regions across MVS™ images in a sysplex.

IRC exploits the cross-system coupling facility (XCF) of MVS and removes the need for z/OS® Communications Server to communicate between MVS images in the same sysplex.

In a sysplex, you must install DFHIRP from the highest release of CICS running in that MVS image.

Sysplex overview

A sysplex consists of multiple MVS systems, coupled together by hardware elements and software services. In a sysplex, MVS provides a platform of basic multisystem services that multisystem applications like CICS can use. As the workload grows, you can add MVS systems to the sysplex to meet the requirements of the greater workload.

To use XCF to communicate in a sysplex, you specify the XCF group name to CICS using the SIT XCFGROUP parameter. The default name is DFHIR000. If you specify a different group name, only members that specify that same group name can communicate using XCF. For more information about XCFGROUP, see XCFGROUP system initialization parameter.

MVS XCF for MRO

When you format the primary and alternate couple data sets used by the XCF component of MVS, make sure that the following conditions are met:
  • The value specified for the MAXMEMBER parameter must be large enough to handle the number of CICS regions and users of the EXCI in the CICS XCF group.
    In a single sysplex, a theoretical maximum number of 1023 CICS regions can participate in XCF/MRO using the same XCF group. However, the maximum size of the XCF group is reduced if you set the MVS MAXMEMBER parameter, used to define XCF couple data sets, to a lower limit. When you calculate the maximum number of members in the CICS XCF group, allow one member for each of these items:
    • Each CICS region to run on an MVS image in the sysplex.
    • Each pipe that is allocated by a user of the external CICS interface (EXCI). For information about EXCI users and pipes, see The EXCI CALL interface.
    To list the members in the CICS XCF group, you can use the MVS DISPLAY command. The name of the CICS group is always DFHIR000, so you can use this MVS command: 
    DISPLAY XCF,GROUP,DFHIR000,ALL
  • The value specified for the MAXGROUP parameter must be large enough for the CICS XCF group to be established.