Digital Data Storage
Digital Data Storage (DDS ) is a magnetic tape storage format for backup and archiving of data, based on the DAT format from the sound. The original DDS format ( subsequently also referred to as DDS-1 ) was developed in 1989 by HP and Sony.
Bands corresponding to the DDS format, can be used both in DAT and DDS drives. However, DDS drives can usually play music neither of DAT cassettes, yet they use to record data.
DDS -1 and DDS - 5 is about 4 mm (3.80 mm) wide is used in a magnetic tape cassette, DDS - 6, it is 8 mm wide. The dimensions of the cassette are ( 73.0 ± 0.3 ) mm × ( 54.0 ± 0.3 ) mm × ( 10.5 ± 0.2 ) mm ( from DDS -6 is 14.7 mm with a bit thicker ). In DDS, the process of helical scanning (English helical scan) is used (such as even with VHS). DDS drives have two read-write heads, the read heads for immediate verification of the written data to use when writing.
The DDS format was mainly in the 1990s one of the most widespread data protection technologies in smaller networks.
DDS drives are usually connected via the SCSI interface, some manufacturers now offer but also DDS drives with the common USB interface.
Despite this standardization, it is not certain that it is a tape that was written with the drive of a manufacturer ( eg Seagate ), with the drive from a different manufacturer (eg Sony) or sometimes even just with a different drive the same type as the original drive can be read in again. So it is advisable to ensure that before disposing of the original backup drive that the backups created can be read on Successor devices (even if this is to be understood according to the specifications / zus see Weblink v. RDE). For this reason, many users consider DDS also no longer as safe enough for archiving, because they can not predict with certainty whether the data is still read when the drive with which they were recorded, was destroyed by a fire, for example,. Generally DDS suffers from the helical recording. Should the mechanics also forgiven only slightly during the useful life and therefore may deviate from the specifications, the tapes are only read by a drive, with which the data was archived.
Standardization
In the course of time, the band length and capacity of the DDS format are again increased. The formats DDS DDS -DC, DDS-2, 3 - DDS and DDS -4 are detailed in the following ECMA and ISO / IEC standards:
The various DDS formats are all backward compatible, so that, for example, a DDS -4 drive can read and write a DDS -1 tape should. In practice, the backward compatibility is not complete. For example, DDS-1 tapes can neither read nor write some DDS -5 drives DDS -1 and DDS-2 and DDS -4 tapes drives.
The development of DDS is done by the DDS / DAT Manufacturers Group.
Capacity
The capacities of the various DDS variants of the following table:
Data compression
All DDS DDS variants since DC allow the use of data compression. The compression and decompression takes place in the drive; the method employed here is a designated as DCLZ variant of LZW, the 11557 under the name Data Compression for Information Interchange as ECMA 151 and ISO / IEC - is normalized DLCZ Algorithm - Adaptive Coding with Embedded Dictionary.
Therefore compressed capacities are often indicated by drive and media manufacturers that accept an optimal compression ratio of 2:1, for example, 24 GB DDS - third However, the actual compression ratio dependent on the data to be compressed; a 2:1 ratio is rarely achieved in practice, particularly in already compressed data. For mixed data (text, images, videos, ...) typically fit about 14-15 GB on a DDS -3 medium.
Service life of the media
The small band format used in DDS leads to very thin support films that are mechanically only limited robustness. Therefore, the format allows only about 25 to more than 100 cycles of use. The recommended maximum storage time is about ten years.