The technology of tape backups DDS (Digital Data
Storage) is the standard defined by HP and Sony for the use of audiotapes DAT as
device backup. The mechanism is the same, but the method of encoding data is
different.
The DAT is a native tape format for
digital audio files with a sampling frequency to 48 kHz. In 1989, Hewlett
Packard and Sony join forces to set the standard DDS arising from this
technology (the same mechanism for readers, but different encoding). The tapes
used are 4 mm wide.
The technique of reading / writing is so
elliptical (the head is not perpendicular to the tape) as for analog videotapes.
It is itself slower than linear. By cons, this method allows for larger
capacities. The writing is done by packets of 128 KB, control correction
included. When reading, the reader reads the entire packet (including the
correction) before writing data to disk.
Two types of backup tapes are used: DDS (most
common) and named DataDate. The system allows DATA DAT writing up to 1 GB in
compressed mode on the cartridge 90 meters (always 4 mm), it is more specialized
to the audio.
Standard
Capacity
Data transfer rate max.
DDS
2 GB
55 KB / s
DDS-1
2 / 4 GB
0,55 / 1,1 MB / s
DDS-2
4 / 8 GB
0,55 / 1,1 MB / s
DDS-3
12 / 24 GB
1,1 / 2,2 MB / s
DDS-4
20 / 40 GB
1,1 / 2,2 MB / s
DDS-5
36/72 GB
1.5 / 3 MB / s
DDS6 (DAT 160)
80/160 GB
3.5 / 6.9 MB /s
DAT
320
160/320 GB
Only the last 2 standards are still used. This
backup system is currently the most widely used server for small businesses in
competition with AIT from Sony. The interface drives in SCSI is 160 or 320 and SAS
(Serial SCSI)
The technique of reading / writing is so
elliptical (the head is not perpendicular to the tape) as for analog videotapes.
It is itself slower than linear. By cons, this method allows for larger
capacities. The writing is done by packets of 128 KB, control correction
included. When reading, the reader reads the entire packet (including the
correction) before writing data to disk.