Abstract: A peripheral data storage subsystem has means for responding to a MOUNT command received from a host processor to create and mount a host-processor-addressable logical data-storage volume. Such logical data-storage volume has a serial number VOLSER indicated in the MOUNT command. The logical data volume is assigned a predetermined area of a physical data volume, such area being termed a partition. The illustrated embodiment shows a tape subsystem in which the partitions are accessed by a control using a reel tachometer that identifies segments of the tape. Each partition has a number of the tape segments. Controls and methods are described for initializing the subsystem for effecting the automatic volume creation, appending data into a logical volume, how logical volumes are made to be portable, moving logical volumes amongst diverse physical media, tape formats usable for such logical volumes, data base control of the logical volumes and volume creation processing.