Common Tape Backup Standards

Tape drives come in a variety of industry-standard as well as some proprietary formats. The following list details several of the available formats:

  • QIC, QIC-Wide, and Travan. Travan is a development of the QIC and QIC-Wide family of low-cost, entry-level tape backup drives. Travan drives can handle data up to 40GB at 2:1 compression.

  • DAT (Digital Audio Tape). This is a newer technology than QIC and its offshoots, and it uses Digital Data Storage (DDS) technology to store data up to 40GB at 2:1 compression (DDS-4) and up to 72GB in the new DDS fifth-generation drives. DAT drives are often referred to as DDS drives for this reason.

  • AIT (Advanced Intelligent Tape). This is becoming the successor to DAT/DDS because it can handle higher capacities than DAT.

  • OnStream's ADR (Advanced Digital Recording) and ADR2. This features a capacity up to 50GB at 2:1 compression and a choice of SCSI, ATA, and popular external interfaces in its 30GB and 50GB (2:1 compression) versions for desktop computers. ADR2 has compressed capabilities up to 120GB (2:1 compression).

  • Exabyte (formerly Ecrix)'s VXA-1 and VXA-2 drives. VXA-1 offers a capacity of 66GB at 2:1 compression and a variety of high-speed SCSI and IEEE-1394 interface options. The VXA-1 format has been approved by the ECMA, an important international organization that establishes standards for information and communication systems. The improved VXA-2 drives have capacities up to 160GB (2:1 compression).

Other tape backup standards, such as DLT (Digital Linear Tape) and 8mm, are used primarily with larger network file servers.

QIC and Its Variants (QIC-Wide and Travan)

The first 1/4'' tape drive was introduced in 1972 by 3M, and it used a cartridge size of 6''x4''x5/8''. This pioneering cartridge established the so-called "DC" data cartridge standard that was used with the first true QIC-standard drive—the 60MB QIC-02, introduced in 1983–1984.

The QIC-02-compatible drives were sold for several years and, like many early tape backup drives, used a dedicated host adapter board. QIC-02's small capacity began to be a problem in the mid-1980s, and many other QIC standards were created for larger drives.

DAT/DDS Tape Drives

Of the many high-performance tape drives on the market, this author's longtime favorite has been the DAT/DDS tape drive family because of its combination of performance, capacity, reliability, and reasonable price. Four levels of DAT/DDS drive capacity are available:

  • DDS-1. This entry-level member of the family (2GB native/4GB at 2:1 compression) is now obsolete.

  • DDS-2. Has the same capacity as drives based on Travan NS8 (4GB native/8GB at 2:1 compression).

  • DDS-3. Has a slightly larger capacity (12GB native/24GB at 2:1 compression) than Travan NS20.

  • DDS-4. Has a 20GB native/40GB at 2:1 compression capacity, which is double the capacity of Travan NS20 and equal to Travan 40GB.

  • DDS Fifth Generation. The newest member of the DAT/DDS family, it has a 36GB native/72GB at 2:1 compression capacity.

Even though DAT/DDS drives are more expensive than Travan drives with similar capacities, the media cost is much lower because of the drive's design. For example, you will pay about three times as much for a Travan NS20 cartridge as for a slightly higher-capacity DDS-3 cartridge.

A DDS-4 cartridge, which offers double the capacity of Travan NS20, still sells for about 30% less. DDS drives are more reliable than Travan or earlier QIC-based drives, which is a vital consideration because the most important reason to use a tape backup is to perform a restore.

The enhanced reliability of DDS drives is aided by the inclusion of automatic head-cleaning features built into most DDS drives and media. After Sony announced in April 2001 that DDS-4 tape drives would be the end of the DAT/DDS lineup of drives, the future of DAT/DDS tapes was uncertain.

However, in January 2003, HP and Seagate RSS announced the development of a fifth generation of DDS drives with higher capacity and backward read/write compatibility. This new format nearly doubles the capacity of DDS-4 and adds several improvements in reliability as well.

AIT Unique Features

Sony's AIT has several unique features designed to make backup and restoration faster and more reliable. An optional Memory In Cassette (MIC) chip allows the cartridge to remember which of the 256 on-tape partitions were used for the data you want to restore, so the correct starting point can be located in seconds.

AIT drives also have a servo tracking system called Auto Tracking Following (ATF), which is used for accurate data-track writing, and Advanced Lossless Data Compression (ALDC), a mainframe-style compression method that can compress data to a greater extent than other methods.

The drives have several other features, including built-in head cleaning that is activated when soft (correctable) errors reach a preset limit, metal-evaporated tape media that avoids head contamination, and a 3 1/2'' form factor.

DLT Unique Features

DLT segments the tape into parallel horizontal tracks and records data by streaming the tape across a single stationary head at 100''–150'' per second during read/write operations.

This is a dramatic contrast to traditional helical-scan technology, in which the data is recorded in diagonal stripes with a rotating drumhead while a much slower tape motor draws the media past the recording head.

The result is a very durable drive and a robust medium. DLT drive heads have a minimum life expectancy of 15,000 hours under worst-case temperature and humidity conditions, and the tapes have a life expectancy of 500,000 passes.

SLR Unique Features

Tandberg's SLR drives use a linear recording method; the tape used by the SLR 40, SLR 60, and SLR 100 is divided into 192 tracks. Twenty-four prewritten servo tracks are used to adjust the position of the read/write head as necessary.

This feature is designed to ensure compatibility of SLR tapes between drives, enabling a tape written by one drive unit to be readable by another unit. Six tracks are written at the same time. The entry-level SLR7 uses a simplified recording method that uses two tracks.

Both tape types have fault-tolerance features that enable the drive to switch to another track for data recording if the original track fails. SLR media is available from most major tape vendors.

Exabyte VXA Unique Features

The Exabyte VXA drives (originally developed by Ecrix, which merged with Exabyte in November 2001) combine special recording and playback methods.

The recording method used somewhat resembles a normal helical scan, but the tape is guided past the magnetic drum with a completely different type of mechanism and the data is recorded at variable speeds that change according to how fast the host can transmit data.

This eliminates the need to wind tape backward because of data underruns (back-hitching). Data is recorded in 64-byte groups of 387 data packets rather than in linear blocks. VXA drives use a special read feature called overscan operation (OSO).

OSO performs redundant reads of each group of data packets, enabling data to be retrievable even from damaged tapes. The packetizing of data works the same way as on the Internet: Data can be read in any order and reassembled into its original form when all packets are received.

In tests, Exabyte and Ecrix have boiled, frozen, and even poured hot coffee over VXA tapes and been able to retrieve 100% of the stored data.

LTO Technology Unique Features

Linear Tape-Open, better known as LTO, is a very high-performance tape backup technology that offers two distinct types of mechanisms:

  • Ultrium. This implementation of LTO is optimized for very high capacities. For example, Ultrium drives have an uncompressed capacity of 100GB (200GB at 2:1 compression) and transfer rates of 20MBps–40MBps. Ultrium Generation 2 drives have an uncompressed capacity of 200GB and transfer rates of 40MBps–80MBps.

Both types of drives also have special features such as dynamic power-down (protects tapes from damage during a power interruption), intelligent data compression, intelligent media analysis to avoid suspect tape areas, and variable tape speed to minimize back-hitching.

Ultrium drives are popular in both single-drive and tape-library formats, although they are quite expensive: Basic single-cartridge units start at around $3,500, with 100GB (uncompressed) cartridges selling for about $80–$90 each.

  • Accelis. This proposed implementation of LTO is optimized for very high speeds, using a dual-reel cartridge that enables tape to be loaded from the mid-point instead of the beginning. It has a native capacity of 25GB (50GB at 2:1 compression) and features cartridge memory and throughput of 20MB–40MB per second.

Because Ultrium drives achieve the same speeds at much higher capacities, it's no surprise that Accelis appears to be an on-paper variation at this point, with no drives on the market using this variation on LTO.