Definition

DLT (digital linear tape)

Contributor(s): Ed Hannan

DLT (digital linear tape) is a magnetic tape and drive system used for computer data storage and archiving. Super DLT (SDLT), a variant that offered high capacity, came on the market in 2001.

History of DLT

Digital Equipment Corp. developed DLT technology in the 1980s and introduced the format for use in its MicroVAX II and PDP-11 minicomputers. The first CompacTape I cartridge used 22 tracks and stored 94 megabytes (MB).

Digital Equipment produced the TK50, TK70, DLT260, DLT600 and DLT2000 formats.

In 1994, the DLT technology was purchased by tape drive manufacturer Quantum Corp. Between 1994 and 2007, Quantum released the DLT2000XT, DLT4000, DLT7000, DLT8000, SDLT 220, SDLT 320, SDLT 600, SDLT 600A, DLT-S4 and DLT-S4A formats. The vendor stopped production on its SDLT line in 2005 with the SDLT 600A drive, but continued to produce DLT drives through 2007. At that point, production sales for DLT had declined due to the greater adoption of Linear Tape-Open (LTO) technology, which hit the market in 2000.

DLT diagram
Diagram of a DLT drive.

Quantum has since adopted the LTO standard, but DLT-V and DLT-S drives and tapes remain available.

DLT vs. SDLT

DLT technology is an adaptation of reel-to-reel tape methodology where the tape cartridge is the source reel and the tape drive is the take-up reel. In a DLT drive, data is written on the tape in dozens of straight-line (linear) tracks -- usually 128 or 208 -- with multiple tracks on half-inch tape. Some cartridges can hold 70 gigabytes (GB) of data when compression is used.

SDLT can store upwards of 100 GB on a single cartridge. A SDLT drive can transfer data at speeds up to 10 megabytes per second (MBps).

DLT vs. SDLT
Illustration of a DLT vs. SDLT cartridge.

DLT drives range in capacity from 10 GB to 40 GB of uncompressed data. A variety of interfaces are used, including proprietary, SCSI, fast SCSI-2, Ultra2-wide SCSI, Gigabit Ethernet (both file transfer protocol and HTTP) and serial-attached storage (SAS). DLT drives can transfer data at speeds up to 60 MBps and offer write once read many (WORM) capability.

DLT and SDLT drives generally offer 1.3:1 to 1.5:1 compression rates, respectively.

DLT4000 cartridges offer the following:

  • Hold 20 GB of data natively, 40 GB compressed
  • Back up at a rate of approximately 10 GB per hour natively and 20 GB per hour compressed

SDLT 320 cartridges offer the following:

  • Hold 160 GB of data natively, 320 GB compressed
  • Back up at a rate of 57.6 GB per hour natively and 115 GB per hour compressed

Examples of competing devices include the advanced intelligent tape (AIT) drive and the Mammoth drive.

DLT manufacturers include Fujifilm, Hitachi, Imation and Sony. Many other companies serve as resellers, including Quantum.

This was last updated in September 2016

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Is there a future for digital linear tape given the stronghold LTO has on the tape storage market?
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