Digital Data Storage
From Wikipedia, the free encyclopedia
Digital Data Storage (DDS) is a format for storing and backing up computer data on magnetic tape that evolved from Digital Audio Tape (DAT) technology, which was originally created for CD-quality audio recording. In 1989, Sony and Hewlett Packard defined the DDS format for data storage using DAT tape cartridges. Tapes conforming to the initial DDS format can be "played" by either DAT or DDS tape machines. However, most DDS tape drives cannot retrieve the audio stored on a DAT cartridge.
DDS uses 3.8 millimeter wide tape. Initially, the tape was 60 or 90 meters long, although advancements in materials technology have allowed the length to be increased significantly in successive versions. A DDS tape drive uses helical scanning for recording, the same process used by a video cassette recorder (VCR). There are two read heads and two write heads. The read heads verify the data that has been written (recorded). If errors are present, the write heads rewrite the data.
A DDS cartridge needs to be retired after 2,000 passes or 100 full backups. Tape drives should be cleaned regularly to be kept in good working order. DDS tapes have an expected life of at least 10 years.
The DDS format competes mainly against the LTO, AIT, VXA, and Travan formats.
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[edit] Generations
| Format | Date | Tape Length (m) | Capacity (GB) | Speed (MB/s) |
|---|---|---|---|---|
| DDS-1 | 1989 | 60/90 | 1.3/2.0 | 0.6 |
| DDS-2 | 1993 | 120 | 4.0 | 0.6 |
| DDS-3 | 1996 | 125 | 12.0 | 1.1 |
| DDS-4 | 1999 | 150 | 20.0 | 3.2 |
| DAT 72 | 2003 | 170 | 36.0 | 3.2 |
| DAT 160 | 2007 | 150 | 80 | 6.9 |
[edit] DDS-1
Stores up to 1.3 GB uncompressed (2.6 GB compressed) on a 60 meter cartridge, 2 GB uncompressed (4GB compressed) on a 90 meter cartridge.
[edit] DDS-2
Stores up to 4 GB uncompressed (8 GB compressed) on a 120 meter cartridge.
[edit] DDS-3
Stores up to 12 GB uncompressed (24 GB compressed) on a 125 meter cartridge. DDS-3 uses PRML (Partial Response Maximum Likelihood). PRML eliminates electronic noise for a cleaner data recording.
[edit] DDS-4
DDS-4 stores up to 20 GB uncompressed (40 GB compressed) on a 150 meter cartridge. This format is also called DAT 40.
[edit] DAT 72
DAT72 stores up to 36 GB uncompressed (72 GB compressed) on a 170 meter cartridge. The DAT 72 standard was developed by HP and Certance. It has the same form-factor and is backwards compatible with DDS-3 and -4.
[edit] DAT 160
DAT 160 was launched in June 2007 by HP. A major change from the previous generations is the width of the tape. DAT 160 uses 8 mm wide tape while all prior versions use 3.81 mm wide tape. Despite the difference in tape widths, DAT 160 drives are backwards compatible with DAT 72 and DAT 40 (DDS-4). Native capacity is 80GB and native transfer rate 6.9MB/s. Launch interfaces are SCSI and USB.
The next drive in the DAT roadmap is the DAT 320.
[edit] Official standards
- ECMA-139 ISO/IEC 10777:1991, Specification of DDS. [1]
- ECMA-146 ISO/IEC 11321:1992, Specification of DATA/DAT. [2]
- ECMA-150 ISO/IEC 11557:1992, Specification of DDS-DC (DDS w/ compression). [3]
- ECMA-151 ISO/IEC 11558:1992, Specification of DCLZ (compression algorithm). [4]
- ECMA-170 ISO/IEC 12447:1993, Specification of DDS (for 60m and 90m tapes). [5]
- ECMA-171 ISO/IEC 12448:1993, Specification of DATA/DAT-DC (for 60m and 90m tapes). [6]
- ECMA-198 ISO/IEC 13923, Specification of DDS-2. [7]
- ECMA-236 ISO/IEC 15521, Specification of DDS-3. [8]
- ECMA-288 ISO/IEC 17462, Specification of DDS-4. [9]
[edit] External links
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