A cluster data set is required if multiple SDMs within a logical partition are to be coupled to a master session through a cluster session. The XRC PARMLIB parameter of ClusterMSession of the STARTUP category is used to activate (enable) a cluster session in a logical partition. The value provided for this parameter indicates the master session name to which SDMs in the logical partition are to be coupled. All SDMs logical partition for which an XCOUPLE add command is issued are to be coupled to the specified master session through the cluster session.
The cluster session and not the individual SDMs in a logical partition continuously write to and read from the master data set. The cluster data set contains information that allows a cluster session to restart if the ANTCLnnn address space terminates (the address space in which the cluster session runs). This information includes the name of the master session with which the cluster session was last associated.