Digital Data Storage (DDS) is the recording format used for computer data storage on Digital Audio Tape (DAT) cartridges using the helical scan method. DAT was developed by Sony for recording high quality digital audio recordings, but only saw limited success, mainly in professional studios.
The Digital Data Storage (DDS) format was defined jointly by Sony and Hewlett Packard for recording data to DAT cartridges. The first generation of computer storage media the DDS-1 was introduced in 1987 with an uncompressed data capacity of 1.3GB. DAT data cartridges are always quoted as having a compression ratio of 2:1, but this is dependent upon the data being recorded.
4mm DAT cartridges
The first 5 generations of the DDS DAT data cartridge are labelled as 4mm data tapes, although it is really on 3.81mm wide media. The earliest couple of generations were prone to alignment issues, with the guide pins coming loose and out of alignment, which could cause issues whereby data could not be read back easily. If left unchecked, it could eventually lead to new data tracks overwriting the previously recorded ones, which would cause serious problems during data recovery.
From the DDS-3 tape drive onwards automatic tracking and better guide pin technology was built into the drives, largely eliminating this as an issue. By the time the DAT 72 (sometimes called DDS-5) the 5th generation drive was introduced in 2003, the uncompressed storage capacity had increased from 1.3GB to 36GB on a single data cartridge.
8mm DAT Cartridges
In 2007 Hewlett Packard released the DAT 160 which was developed to use 8mm tape media, allowing for significantly higher storage capacity, in this instance 80GB uncompressed. In 2009 the DAT 320 with double the storage capacity was introduced.
In order to house the larger tape width the cartridge is larger than its 4mm predecessor, although the DAT 160 tape drive provides backwards read/write compatibility with DAT 72 and DDS-4 tapes. The DAT 320 drive is only compatible with its predecessor the DAT 160. The release of the 8th generation has yet to be announced, but a 2012 announcement has planned to be able to store 300GB uncompressed.
DAT Data Recovery
The most common reasons to require data recovery from a DAT data cartridge falls into 3 categories, these being, physical failure, logical data issues or user errors. The physical problems include tape media flaws, unreadable media, snapped tape and de-spooled media. Logical issues relate to corruption of the tape backup and restore failures.
User errors from reinitialising the tape will usually result in some loss of data, although some backup formats which store metadata at the front of the tape, may sometimes allow all files to be recovered. Overwriting a previous backup will lead to some loss of data, the extent of which is totally dependent upon how much data has been backed up.