Coupled Extended Remote Copy (CXRC) support is also referred to as coupled system data movers (SDMs). The coupled support allows multiple XRC sessions to be combined into a single logical session. With CXRC, multiple SDMs coordinate their consistency group processing such that the recovery of all secondary volumes can be done to a single point of consistency. A system data mover will not write data to secondary devices that have a timestamp that is past the time that all SDMs have written to journal data sets.
With CXRC, an XRC environment can be scaled to support configurations significantly greater than that possible with a single SDM. You can couple a maximum of 14 SDMs. If clustering is enabled through the PARMLIB parameter of ClusterMSession, and there are sufficient processor and memory resources to handle peak workload, CXRC can manage up to 182 SDMs, where a single OS/390® or z/OS® image (a logical partition when in LPAR mode) can have a single cluster session managing up to 13 SDMs. Each cluster session acts as a single SDM to CXRC.
In defining a CXRC configuration, each SDM is set up as if it is a stand-alone independent SDM. To couple the XRC sessions, issue the XCOUPLE command to each of session.If clustering is enabled, the system is able to couple the individual XRC session specified on the XCOUPLE command to the master session through the cluster session within an LPAR. A cluster session represents a single SDM in a master session.In addition, a CXRC configuration requires a master data set, which is accessible by the SDMs. If you want to couple XRC sessions through a cluster session, a CXRC configuration requires a cluster data set.