A step can include a data set that the program might not use. To
ask the system not to mount the volume for the data set until the
data set is opened, code:
//ddname DD UNIT=(xxxx,,DEFER),...
Deferred mounting can save the operator time.
Example: //MYDS DD DSNAME=DATA5,UNIT=(TAPE,,DEFER)
Note: You can also use deferred mounting for SMS-managed data sets.