Abstract: A tape storage and retrieval system is provided to facilitate the archival of machine data to tape and optionally to disk storage in a manner which enables the retrieval of the data in a batch or on-line processing environment. A hierarchy of storage levels is adopted for data objects within the system. The manner of the storage of the data object within the tape system is determined by the storage level which is changed over time to reflect the need for access to the data object. For example, those tapes storing data object allocated the highest level of storage may be stored in parallel on disks, may only be written so as to occupy only part of the tape volume, or stored on the tape system drive.