Data Sets › Multi-Data Set Volumes

Multi-Data Set Volumes

A multi-data set volume refers to a tape that contains more than one physical data set. Multiple data sets on a tape volume are often referred to as stacked data sets.

CA 1 keeps information concerning all data sets on a tape volume by using a special record, a Data Set Name Block (DSNB), for each secondary data set. The DSNBs are then chained together by pointers, as shown in the following figure. Secondary data sets are listed on the appropriate reports.

Each DSNB record for secondary files stores the expiration date used when the file was created. During multifile creation, if a numerically higher expiration date is presented for a secondary file, the Volume record for the first file is updated with the higher expiration date, and this becomes the controlling expiration date. With ANSI-labeled tapes, IBM does not permit the expiration date for a secondary file to exceed the expiration date for any previous data set on the volume.