Cartridge-type tapes, associated with 3480 and later tape devices, are always written in single file format, except when they are used as dump tapes. Single file format provides performance advantages for migration and backup processing because it reduces I/O and system serialization. Additionally, single file format provides better recovery for tapes that are partially overwritten or that have become unreadable, because the AUDIT MEDIACONTROLS and TAPECOPY commands work only with single file format tapes.

Single file format reduces I/O and system serialization, because only one label is required for each connected set (as opposed to multiple file format tapes that require a label for each data set). The standard-label tape data set that is associated with the connected set can span up to the allocation limit of 255 tapes. It is possible that HSM could extend the connected set beyond 255 tapes via subsequent backup or migration processing if the last volume was not marked full. This standard-label tape data set is called the DFSMShsm tape data set. Each user data set is written, in 16K logical blocks, to the DFSMShsm tape data set. A single user data set can span up to 254 tapes.

After DFSMShsm writes a user data set to tape, it checks the volume count for the DFSMShsm tape data set. If the volume count is greater than 240, the DFSMShsm tape data set is closed, and the currently mounted tape is marked full and is deallocated. DFSMShsm selects another tape, and then starts a different DFSMShsm tape data set. Data set spanning can be reduced using the SETSYS TAPESPANSIZE command.

Single file format tapes support full DFSMShsm function because they support the tape-copy, tape-replace, and duplex functions of DFSMShsm (multiple file format tapes do not).