//SORTIN   DD  DSN=SORTIN,DISP=(OLD,KEEP),UNIT=3490,
//                VOL=SER=(75836,79661,72945)

If the input data set is contained on more than one reel of magnetic tape, the VOLUME parameter must be included on the SORTIN DD statement to indicate the serial numbers of the tape reels. In this example, the input data set is on three reels that have serial numbers 75836, 79661, and 72945.

If a data set is not on a disk or on a standard-labeled tape, you must specify DCB parameters in its DD statement.