Digital Linear Tape
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Digital Linear Tape (DLT) is a magnetic tape technology used for computer data storage. It was invented by Digital Equipment Corporation in 1984, and was purchased by Quantum Corporation in 1994, who currently manufactures drives and licenses the technology and trademark.
A variant with higher capacity is called Super DLT (SDLT). The lower cost "value line" was initially manufactured by Benchmark Storage Innovations. Quantum acquired Benchmark in 2002.
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[edit] Technology
DLT uses linear serpentine recording with multiple tracks on half-inch (12.6 mm) wide tape. The cartridges contain a single reel and the tape is pulled out of the cartridge by means of a leader tape attached to the takeup reel inside the drive. The drive leader tape is buckled to the cartridge leader during the load process. Tape speed and tension are controlled electronically via the reel motors; there is no capstan. The tape is guided by 4 to 6 rollers that touch only the back side of the tape. Tape material is metal particle tape (MP/AMP.)
SDLT adds an optical servo system that reads servo patterns on the back of the tape, in order to keep the data tracks on the front of the tape correctly aligned with the read/write heads. This is important for newer tape media, which have very thin dense data tracks; 256, 384 and 768 data tracks on a half inch wide tape are now common.
DLT7000 and 8000 tilt the head forward and backward to reduce crosstalk between adjacent tracks through azimuth; this is called Symmetric Phase Recording.
All (S)DLT drives support hardware data compression. The often-used compression factor of 2:1 is optimistic and generally only achievable for text data; a more realistic factor across a file system is 1.3:1 to 1.5:1.
Media are guaranteed for 30 years of data retention under specified environmental conditions; however, they are easily damaged by mishandling (dropping or improper packaging during shipment.)
Current manufacturers of cartridges for the DLT/SDLT market are Fujifilm, Hitachi/Maxell and Imation. VStape is made by Sony. All other companies/brands (even Quantum) are contractors and/or resellers of these companies.
A new naming convention took effect in 2005, calling the performance line DLT-S and the value line DLT-V.
[edit] Generations
[edit] Drives
Standard | Capacity (GB) | Interface | Data Rate (MB/s) | Date | Media |
---|---|---|---|---|---|
TK50/TZ30 | 0.1 | proprietary/SCSI | 0.045 | 1984 | CT I |
TK70 | 0.3 | proprietary | 0.045 | 1987 | CT II |
THZ01/DLT260/Tx85 | 2.6 | DSSI/SCSI | 0.8 | 1989 | DLT III |
THZ02/DLT600/Tx86 | 6 | DSSI/SCSI | 0.8 | 1991 | DLT III |
DLT2000/Tx87 | 10 | Fast SCSI-2 | 1.25 | 1993 | DLT III |
DLT2000XT | 15 | Fast SCSI-2 | 1.25 | 1995 | DLT IIIXT |
DLT4000/Tx88 | 20 | Fast SCSI-2 | 1.5 | 1994 | DLT IV |
DLT7000/Tx89 | 35 | Fast/Wide SCSI-2 | 5 | 1996 | DLT IV |
DLT8000 | 40 | Fast/Wide SCSI-2 | 6 | 1999 | DLT IV |
SDLT 220 | 110 | Ultra-2 | 10 | 1998 | SDLT I |
SDLT 320 | 160 | Ultra-2 | 16 | 2002 | SDLT I |
SDLT 600 | 300 | Ultra-160/FC 2Gb | 36 | 2004 | SDLT II |
SDLT 600A | 300 | GbE (FTP, HTTP) | 36 | 2005 | SDLT II |
DLT-S4 | 800 | Ultra-320/FC 4Gb/SAS | 60 | 2006 | S4 |
DLT-S5 | 1500? | 100? | |||
Value line | |||||
DLT1 | 40 | Fast/Wide SCSI-2 | 3 | 1999 | DLT IV |
DLT-VS80 | 40 | Fast/Wide SCSI-2 | 3 | 2001 | DLT IV |
DLT-VS160 | 80 | Ultra-2 | 8 | 2003 | VS1 |
DLT-V4 | 160 | Ultra-160/SATA | 10 | 2005 | VS1 |
DLT-V5 | 250? | 18? |
[edit] Media
Name | Formats | Color | Supported by |
---|---|---|---|
CompacTape I | 0.1 | Gray | TK50/70 |
CompacTape II | 0.3 | Gray | TK70 |
DLTtape III | 2.6, 6, 10 | Light brown | DLT260/600, DLT2000/2000XT/4000/7000 |
DLTtape IIIXT | 15 | White | DLT2000XT/4000/7000/8000 |
DLTtape IV | 20, 35, 40 | Dark brown | DLT4000/7000/8000, SDLT220/320 (ro) |
Cleaning Tape III | 20 cleans | Beige | DLT2000/2000XT/4000/7000/8000 |
SDLTtape I | 110, 160 | Dark green | SDLT220/320, SDLT600 (ro), DLT-S4 (ro) |
SDLTtape II | 300 | Dark blue | SDLT600, DLT-S4 (ro) |
DLTtape S4 | 800 | Dark purple | DLT-S4 |
SDLT Cleaning Tape | 20 cleans | Light gray | SDLT220/320/600, DLT-S4 |
DLTtape VS1 | 80, 160 | Ivory/Black | VS160, DLT-V4, SDLT600 (ro) |
DLT VS Cleaning Tape | 20 cleans | Brown | DLT1, DLT-VS80 |
DLT VS160 Cleaning Tape | 20 cleans | Light gray | DLT-VS160, DLT-V4 |
Tapes written in value series drives can typically be read (and often written) in higher end drives of a similar vintage. Check the specs for your specific drive to find out its interoperability options.
[edit] External links
- History of DLTtape™ Technology, from TK50 1984 to SDLT1 2001
- DLTtape™ Handbook, 8th ed. (Quantum 2001) (PDF)
- DLT Roadmap at dlttape.com
- Quantum Corp. DLT drive page
- Obituary of Dr. Fred Hertrich, "father" of DLT
[edit] Standards
- ECMA 197 Specification of DLT 2. [1]
- ECMA 209 Specification of DLT 3. [2]
- ECMA 231 Specification of DLT 4. [3]
- ECMA 258 Specification of DLT 3-XT. [4]
- ECMA 259 Specification of DLT 5. [5]
- ECMA 286 Specification of DLT 6. [6]
- ECMA 320 Specification of SDLT-1. [7]
Magnetic tape data storage formats | ||
---|---|---|
Linear | Helical-Scan | |
Three Quarter Inch (~19 mm) |
||
Half Inch (12.65 mm) |
UNISERVO (1951) - IBM 7 Track (1952) - IBM 9 Track (1964) - IBM 3480 (1984) - DLT (1984) - IBM 3590 (1995) - T9840 (1998) - T9940 (2000) - LTO Ultrium (2000) - T10000 (2006) |
Redwood SD-3 (1995) - DTF (19xx) - SAIT (2003) |
Eight Millimeter (8 mm) |
Travan (1995) - IBM 3570 MP (1997) |
|
Quarter Inch (6.35 mm) |
||
Four Millimeter (3.8 mm) |
DDS/DAT (1989) |
|
One Eighth Inch (3.18 mm) |
KC Standard, Compact Cassette (1975) - Datassette (1977) |
|
Stringy (1.58 - 1.9 mm) |
Exatron Stringy Floppy (1979) - ZX Microdrive (1983) - Rotronics Wafadrive (1984) |