Digital Linear Tape
Encyclopedia
Digital Linear Tape (previously called CompacTape) is a magnetic tape data storage
technology developed by Digital Equipment Corporation
(DEC) from 1984 onwards. In 1994 the technology was purchased by Quantum Corporation, 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 under license from Quantum. Quantum acquired Benchmark in 2002.
and PDP-11
minicomputer
s in 1984. This used 22-track CompacTape I cartridges, storing 94 MB per cartridge. The TK50 was superseded in 1987 by the TK70 drive and the 48-track CompacTape II cartridge, capable of storing 294 MB. In 1989, the CompacTape III (later DLTtape III) format was introduced, increasing the number of tracks to 128 and capacity to 2.6 GB. Later drives improved the data density of the DLTtape III cartridge into the early 1990s, up to 10 GB. The DLTtape IV cartridge was introduced by Quantum in 1994, with increased tape length and data density, initially offering 20 GB per tape. Super DLTtape, originally capable of up to 110 GB, was launched in 2001.
s 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 1/2 in 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. Note that drive compression applied to pre-compressed data can actually make the written data larger than having compression turned off in the tape drive.
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.
DLT includes Write Once Read Many
(WORM) capability.
In February 2007, Quantum stopped developing the next generations of DLT drives (S5 and V5) after insufficient market acceptance of the S4 and V4 drives, shifting its drive strategy to LTO
.
DLTtape IV can support both DLT4000/7000/8000 and DLT1/DLT-VS80 for full functions, however, once DLTtape IV media has been written to or formatted in a DLT7000/8000 drive, this media cannot be read, written to, or formatted in a DLT1/DLT-VS80 drive unless it is degaussed. Once the media has been written to or formatted in a DLT4000 drive, the media cannot be written to or formatted in a DLT1/DLT-VS80 drive unless it is degaussed but it can be read. This is because the DLT1/VS series use a different recording format that is not fully supported by the other family.
Tapes written in value series drives can typically be read (and often written to) in higher end drives of a similar vintage. The drive's technical specifications should contain interoperability options.
Magnetic tape data storage
Magnetic tape data storage uses digital recording on to magnetic tape to store digital information. Modern magnetic tape is most commonly packaged in cartridges and cassettes. The device that performs actual writing or reading of data is a tape drive...
technology developed by Digital Equipment Corporation
Digital Equipment Corporation
Digital Equipment Corporation was a major American company in the computer industry and a leading vendor of computer systems, software and peripherals from the 1960s to the 1990s...
(DEC) from 1984 onwards. In 1994 the technology was purchased by Quantum Corporation, 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 under license from Quantum. Quantum acquired Benchmark in 2002.
History
DEC launched the TK50 tape drive for the MicroVAX IIMicroVAX
The MicroVAX was a family of low-end minicomputers developed and manufactured by Digital Equipment Corporation . The first model, the MicroVAX I, was introduced in 1984...
and PDP-11
PDP-11
The PDP-11 was a series of 16-bit minicomputers sold by Digital Equipment Corporation from 1970 into the 1990s, one of a succession of products in the PDP series. The PDP-11 replaced the PDP-8 in many real-time applications, although both product lines lived in parallel for more than 10 years...
minicomputer
Minicomputer
A minicomputer is a class of multi-user computers that lies in the middle range of the computing spectrum, in between the largest multi-user systems and the smallest single-user systems...
s in 1984. This used 22-track CompacTape I cartridges, storing 94 MB per cartridge. The TK50 was superseded in 1987 by the TK70 drive and the 48-track CompacTape II cartridge, capable of storing 294 MB. In 1989, the CompacTape III (later DLTtape III) format was introduced, increasing the number of tracks to 128 and capacity to 2.6 GB. Later drives improved the data density of the DLTtape III cartridge into the early 1990s, up to 10 GB. The DLTtape IV cartridge was introduced by Quantum in 1994, with increased tape length and data density, initially offering 20 GB per tape. Super DLTtape, originally capable of up to 110 GB, was launched in 2001.
Technology
DLT uses linear serpentine recording with multiple tracks on half-inch (12.7 mm) wide tape. The cartridgeCartridge
Cartridge may refer to:* 8-track tape cartridge, a 1960s-1980s music storage format* Broadcast cartridge used in radio stations* Cartridge , a round of ammunition* Cartridge...
s contain a single reel
Reel
A reel is an object around which lengths of another material are wound for storage. Generally a reel has a cylindrical core and walls on the sides to retain the material wound around the core...
and the tape
Magnetic tape
Magnetic tape is a medium for magnetic recording, made of a thin magnetizable coating on a long, narrow strip of plastic. It was developed in Germany, based on magnetic wire recording. Devices that record and play back audio and video using magnetic tape are tape recorders and video tape recorders...
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
Visual Servoing
Visual servoing, also known as Vision-Based Robot Control and abbreviated VS, is a technique which uses feedback information extracted from a vision sensor to control the motion of a robot. One of the earliest papers that talks about visual servoing was from the SRI International Labs. A first...
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 1/2 in 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
Symmetric Phase Recording
Tape recording technology developed by Quantum Corporation packs data across a tape's recording surface by writing adjacent tracks in a herringbone pattern: track 0 = \\\\\, track 1 = /////, track 2 = \\\\\, track 3 = /////, etc....
.
All (S)DLT drives support hardware data compression
Data compression
In computer science and information theory, data compression, source coding or bit-rate reduction is the process of encoding information using fewer bits than the original representation would use....
. 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. Note that drive compression applied to pre-compressed data can actually make the written data larger than having compression turned off in the tape drive.
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
Fujifilm
is a multinational photography and imaging company headquartered in Tokyo, Japan.Fujifilm's principal activities are the development, production, sale and servicing of color photographic film, digital cameras, photofinishing equipment, color paper, photofinishing chemicals, medical imaging...
, Hitachi/Maxell
Maxell
, commonly known as Maxell, is a Japanese company which manufactures consumer electronics. The company's notable products are batteries -- the company's name is a contraction of "maximum capacity dry cell" -- and recording media, including audio cassettes and blank VHS tapes, and recordable optical...
and Imation
Imation
Imation is a US based multi-national technology corporation that designs, manufactures and sells recordable data storage media, consumer electronics products and accessories.The company is a 1996 spin off of 3M and is headquartered in Oakdale, Minnesota...
. VStape is made by Sony
Sony
, commonly referred to as Sony, is a Japanese multinational conglomerate corporation headquartered in Minato, Tokyo, Japan and the world's fifth largest media conglomerate measured by revenues....
. 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.
DLT includes Write Once Read Many
Write Once Read Many
A Write Once Read Many or WORM drive is a data storage device where information, once written, cannot be modified. On ordinary data storage devices, the number of times data can be modified is not limited, except by the rated lifespan of the device, as modification involves physical changes that...
(WORM) capability.
In February 2007, Quantum stopped developing the next generations of DLT drives (S5 and V5) after insufficient market acceptance of the S4 and V4 drives, shifting its drive strategy to LTO
Linear Tape-Open
Linear Tape-Open is a magnetic tape data storage technology originally developed in the late 1990s as an open standards alternative to the proprietary magnetic tape formats that were available at the time. Hewlett-Packard, IBM and Seagate initiated the LTO Consortium, which directs development...
.
Drives
| Drive | 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 Digital Storage Systems Interconnect The Digital Storage Systems Interconnect is a bus developed by Digital Equipment Corporation for connecting storage devices and clustering VAX systems and support was extended to MIPS based DECsystem and later to Alpha processor based AlphaServer systems.It was introduced in 1988 and has a... /SCSI SCSI Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it... |
0.8 | 1989 | DLT III |
| THZ02/DLT600/Tx86 | 6 | DSSI Digital Storage Systems Interconnect The Digital Storage Systems Interconnect is a bus developed by Digital Equipment Corporation for connecting storage devices and clustering VAX systems and support was extended to MIPS based DECsystem and later to Alpha processor based AlphaServer systems.It was introduced in 1988 and has a... /SCSI SCSI Small Computer System Interface is a set of standards for physically connecting and transferring data between computers and peripheral devices. The SCSI standards define commands, protocols, and electrical and optical interfaces. SCSI is most commonly used for hard disks and tape drives, but it... |
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-Wide SCSI | 11 | 1998 | SDLT I |
| SDLT 320 | 160 | Ultra-2-Wide SCSI | 16 | 2002 | SDLT I |
| SDLT 600 | 300 | Ultra-160 SCSI/FC Fibre Channel Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards... 2Gb |
36 | 2004 | SDLT II |
| SDLT 600A | 300 | GbE Gigabit Ethernet Gigabit Ethernet is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second , as defined by the IEEE 802.3-2008 standard. It came into use beginning in 1999, gradually supplanting Fast Ethernet in wired local networks where it performed... (FTP File Transfer Protocol File Transfer Protocol is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server... , HTTP) |
36 | 2005 | SDLT II |
| DLT-S4 | 800 | Ultra-320 SCSI/FC Fibre Channel Fibre Channel, or FC, is a gigabit-speed network technology primarily used for storage networking. Fibre Channel is standardized in the T11 Technical Committee of the InterNational Committee for Information Technology Standards , an American National Standards Institute –accredited standards... 4Gb/SAS Serial Attached SCSI Serial Attached SCSI is a computer bus used to move data to and from computer storage devices such as hard drives and tape drives. SAS depends on a point-to-point serial protocol that replaces the parallel SCSI bus technology that first appeared in the mid 1980s in data centers and workstations,... |
60 | 2006 | S4 |
| DLT-S4A | 800 | GbE Gigabit Ethernet Gigabit Ethernet is a term describing various technologies for transmitting Ethernet frames at a rate of a gigabit per second , as defined by the IEEE 802.3-2008 standard. It came into use beginning in 1999, gradually supplanting Fast Ethernet in wired local networks where it performed... (FTP File Transfer Protocol File Transfer Protocol is a standard network protocol used to transfer files from one host to another host over a TCP-based network, such as the Internet. FTP is built on a client-server architecture and utilizes separate control and data connections between the client and server... , HTTP) |
60 | 2007 | S4 |
| 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-Wide SCSI | 8 | 2003 | VS1 |
| DLT-V4 | 160 | Ultra-160 SCSI/SATA Serial ATA Serial ATA is a computer bus interface for connecting host bus adapters to mass storage devices such as hard disk drives and optical drives... /USB |
10 | 2005 | VS1 |
Media
| Name | Formats (GB) | Color | Supported by (ro=read only) |
|---|---|---|---|
| CompacTape I | 0.1 | Gray | TK50/TZ30, TK70 (ro) |
| 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, DLT1/DLT-VS80, 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 |
DLTtape IV can support both DLT4000/7000/8000 and DLT1/DLT-VS80 for full functions, however, once DLTtape IV media has been written to or formatted in a DLT7000/8000 drive, this media cannot be read, written to, or formatted in a DLT1/DLT-VS80 drive unless it is degaussed. Once the media has been written to or formatted in a DLT4000 drive, the media cannot be written to or formatted in a DLT1/DLT-VS80 drive unless it is degaussed but it can be read. This is because the DLT1/VS series use a different recording format that is not fully supported by the other family.
Tapes written in value series drives can typically be read (and often written to) in higher end drives of a similar vintage. The drive's technical specifications should contain interoperability options.
External links
- Information about Quantum products from Official UK Dealer, Craystone
- History of DLTtape Technology, from TK50 1984 to SDLT1 2001
- DLTtape Handbook, 8th ed. (Quantum 2001) (PDF)
- How to rethread a dropped leader
- DLT Roadmap at dlttape.com
- White Paper: Tape at Risk by Quotium Technologies
- Quantum Corp. DLT drive page
- Obituary of Dr. Fred Hertrich, "father" of DLT
- Storage Heaven TapeMaster DLT Tape Duplication Copiers and Erasers
Standards
- ECMA 197 Specification of DLT 2. http://www.ecma-international.org/publications/files/ecma-st/ECMA-197.pdf
- ECMA 209 Specification of DLT 3. http://www.ecma-international.org/publications/files/ecma-st/ECMA-209.pdf
- ECMA 231 Specification of DLT 4. http://www.ecma-international.org/publications/files/ecma-st/ECMA-231.pdf
- ECMA 258 Specification of DLT 3-XT. http://www.ecma-international.org/publications/files/ecma-st/ECMA-258.pdf
- ECMA 259 Specification of DLT 5. http://www.ecma-international.org/publications/files/ecma-st/ECMA-259.pdf
- ECMA 286 Specification of DLT 6. http://www.ecma-international.org/publications/files/ecma-st/ECMA-286.pdf
- ECMA 320 Specification of SDLT-1. http://www.ecma-international.org/publications/files/ecma-st/ECMA-320.pdf