Multivolume data sets, are data sets that span more than one physical volume. The data sets are protected individually as soon as each volume is created. Multivolume data sets are chained together with backward and forward pointers in the TMC record.
An additional feature of multivolume processing occurs on input for either NL or SL. The volumes must be mounted in the sequence in which they were created. This assures proper processing even when the operator mounts the wrong tape, or when the volume serial numbers are specified in the wrong order in the JCL statement or in the system catalog.
Updates to TMC records for multivolume data sets are through CA 1 online or batch utilities. For some fields such as EXPDT, it must be done only to the first volume. The update is then automatically applied to all volumes of the data set. Updates to fields pertaining to the tape volume only, not the data set, can be made to the single Volume record. System responses to updates for other than the first volume specify the first volume serial number of the set.
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