Digital data storage
| Storage medium Digital Data Storage (DDS)
|
|
 DDS2 cassette |
|
| General | |
|---|---|
| Type | Magnetic tape |
| capacity | 1.3 - 160 GB |
| lifespan | about 10 years |
| size | 73 mm × 54 mm × 10.5 mm (2 7/8 ″ × 2 1/8 ″ × 13/32 ″) DDS1 - DDS5 |
| use | data backup |
| origin | |
| developer | HP , Sony |
Digital Data Storage ( DDS ) is a magnetic tape storage format for backing up and archiving data that is based on the DAT format from audio engineering . The original DDS format (later also referred to as DDS-1) was developed by HP and Sony in 1989 . DDS is a standardized industry standard (ECMA-139).
Tapes that conform to the DDS format can be used in both DAT and DDS drives. 60m corresponds to 120 minutes of audio. However, DDS drives can usually neither play music from DAT cartridges nor use them for data recording. However, there are firmware variants that make some DDS drives DAT-capable. This enables audio DATs to be read in quickly.
The DDS-1 to DDS-5 use a 3.81 mm (0.150 ″) wide magnetic tape in a cassette. For DDS (1-5), the cassette housing measures 73.0 mm × 54.0 mm × 10.5 mm. The tape and the cassette were taken over 1: 1 from the digital audio tape (DAT), which in turn inherited the bandwidth from the compact cassette . From DDS-6 the tape is 8 mm wide and the cassette is slightly thicker at 14.7 mm. In DDS, the process being helical recording (engl. Helical scan ) is used (such as, for example, even when VHS ). DDS drives have two read and write heads each, whereby the read heads are used to immediately check the written data when writing.
The DDS format was one of the most widespread data backup technologies in smaller networks , especially in the 1990s .
DDS drives are usually connected via the SCSI interface, but some manufacturers now also offer DDS drives with the common USB interface.
Despite standardization, it is not certain that a tape that was written to with a drive from one manufacturer (e.g. Seagate), a drive from another manufacturer (e.g. Sony) or sometimes even just another drive of the same design as the original drive. It is therefore advisable to ensure before disposing of the original backup drive that the backups created can be read on the successor devices (even if this should be a matter of course according to the specifications / see additional web link v. RDE). For this reason, many users no longer consider DDS to be safe enough for archiving, as they cannot predict with certainty whether the data can still be read out if the drive with which it was recorded, e.g. B. was destroyed by fire. In general, DDS suffers from oblique recording. Should the mechanics warp even slightly during the period of use and thus deviate from the specifications, the tapes can only be read with the one drive with which the data was archived.
Normalization
Over time, the tape lengths and capacity of the DDS format have increased again and again. The formats DDS, DDS-DC, DDS-2, DDS-3 and DDS-4 are specified in the following ECMA and ISO / IEC standards:
- ECMA-139 (1990) , ISO / IEC 10777: 3.81 mm Wide Magnetic Tape Cartridge for Information Interchange - Helical Scan Recording - DDS format
- ECMA-150 (1991) , ISO / IEC 11557: 3.81 mm Wide Magnetic Tape Cartridge for Information Interchange - Helical Scan Recording - DDS-DC Format using 60 m and 90 m Length Tapes, 2nd Edition
- ECMA-170 (1992) , ISO / IEC 12247: 3.81 mm Wide Magnetic Tape Cartridge for Information Interchange - Helical Scan Recording - DDS Format using 60 m and 90 m Length Tapes
- ECMA-198 (1995) , ISO / IEC 13923: 3.81 mm Wide Magnetic Tape Cartridge for Information Interchange - Helical Scan Recording - DDS-2 Format using 120 m Length Tapes
- ECMA-236 (1996) , ISO / IEC 15521: 3.81 mm Wide Magnetic Tape Cartridge for Information Interchange - Helical Scan Recording - DDS-3 Format using 125 m Length Tapes
- ECMA-288 (1999) , ISO / IEC 17462: 3.81 mm Wide Magnetic Tape Cartridge for Information Interchange - Helical Scan Recording - DDS-4 Format using 150 m Length Tapes
The various DDS formats are downwardly compatible to a limited extent - as a rule, the previous generation can also be used, sometimes also the previous generation, but possibly only read.
The further development of DDS has been stopped.
capacity
The capacities of the different DDS variants can be found in the following table:
| default | Tape length | Capacity (uncompressed) |
Transfer rate |
|---|---|---|---|
| DDS | 60 m | 1.3 GB | 183 kB / s |
| DDS-DC | 90 m | 2.0 GB | 183 kB / s |
| DDS-2 | 120 m | 4.0 GB | 360-750 kB / s |
| DDS-3 | 125 m | 12.0 GB | 0.7-1.5 MB / s |
| DDS-4 | 150 m | 20.0 GB | 1.0-3.0 MB / s |
| DDS-5 (DAT72) | 170 m | 36.0 GB | 3.0 MB / s |
| DDS-6 (DAT160) | 150 m | 80.0 GB | 6.9-13.8 MB / s |
| DDS-7 (DAT320) | 153 m | 160.0 GB |
Data compression
All DDS variants since DDS-DC allow the use of data compression . The compression and decompression takes place in the drive; The method used is a variant of the LZW method called DCLZ , which is standardized as ECMA 151 and ISO / IEC 11557 under the name Data Compression for Information Interchange - Adaptive Coding with Embedded Dictionary - DLCZ Algorithm .
Therefore, drive and media manufacturers often specify compressed capacities that assume an optimal compression ratio of 2: 1, e.g. B. 24 GB for DDS-3. The actual compression ratio depends on the data to be compressed; however, a ratio of 2: 1 is rarely achieved in practice, especially not with data that has already been compressed. With mixed data (text, images, videos, ...) typically around 14-15 GB fit on a DDS-3 medium.
Life of the media
The small tape format used by DDS leads to very thin carrier films that can only be mechanically stressed to a limited extent. The format therefore only allows about 25 to a maximum of 100 usage cycles. The recommended maximum storage period is around ten years.
See also
credentials
- ↑ ECMA website with a link to the standard (PDF) ; accessed on October 14, 2017
- ↑ Computeall: Digital Audio Tape (DAT) FAQ , April 13, 2017
- ↑ nominal 3.81 mm (+0.00 mm −0.02 mm)
- ↑ 73.0 ± 0.3 mm × 54.0 ± 0.3 mm × 10.5 ± 0.2 mm
- ↑ HP StorageWorks DDS / DAT Media - DDS / DAT Media Compatibility Matrix . Hewlett Packard Enterprise. 2016. Retrieved April 13, 2017.
- ↑ Standard ECMA-151 ( English ) Ecma International. Retrieved March 13, 2019.
