When a backup or migration task ends, the last tape is usually only partially filled. When new processing begins, DFSMShsm selects that last partially-filled tape on which to continue processing. This lets you completely fill your tapes, but it does require a specific tape mount.

DFSMShsm allows you to specify that your partially-filled tapes be marked as full. Then, when new processing begins, DFSMShsm issues a nonspecific tape mount, which is beneficial when using cartridge loaders.

If you are not using the duplex tape function, marking partially-filled tapes as full has another benefit. If you want to copy the migration and backup tapes for the purpose of disaster backup protection, marking a tape full allows it to be copied by the generic TAPECOPY command. A partially-filled tape that is not marked as full is not eligible to be copied. The data on the partially-filled tape would not have a disaster backup copy until the next time tape migration and backup processing occurred, the tape was filled, and the TAPECOPY command was run.

If you are using the duplex tape function, even partially-filled migration and backup tapes have copies. Marking partially-filled tapes as full would still provide the benefit of nonspecific tape mounts.

Each installation should weigh the benefits of marking partially-filled tapes as full against the benefits of utilizing the full storage capacity of the tapes, and decide what works best for them.