When you want to store a data set on unlabeled tape volumes, the system needs a volume serial number to identify each volume. If the data set is in an automatic tape library, the system uses the volume serial number that is encoded in the bar code on the outside of each cartridge. If the data set is not in an automatic tape library, it is advisable to specify enough volume serial numbers to contain the data set. If you do not specify any volume serial numbers or do not specify enough of them, the system or a tape management system assigns a serial number to each unidentified volume. If the system assigns a serial number, the serial number is in the form Lxxxyy, in which xxx is the data set sequence number and yy is the volume sequence number for the data set.

If you want to catalog or pass data sets that reside on unlabeled volumes, specify the volume serial numbers for the required volumes. Specifying the volume serial numbers ensures that data sets residing on multiple volumes are not cataloged or passed with duplicate volume serial numbers. Retrieving such data sets can give unpredictable errors.