DEFER specification - Key = '006C'
DALDEFER specifies that the system should allocate a device to the data set, but the volume(s) on which the data set resides should not be mounted until the data set is opened.
When you code DALDEFER, # must be zero; LEN and PARM are not specified. See z/OS MVS JCL Reference for the rules regarding the use of DEFER.
Example: To specify a request for deferred mounting: of
a volume or volumes, code
KEY # LEN PARM
006C 0000 - -