Tape Formats

By Davis D. Janowski  |  Posted 2003-03-11 Print this article Print

Tape Formats

This story focuses on the midrange tape market, which targets small to midsize businesses with up to 400 employees. Two tape technology standards, Linear Tape–Open (LTO) and Super Digital Linear Tape (SDLT), dominate the market. A third technology weve reviewed in this story is Sonys AIT-3 format, which has a small but growing market share and interests us with its very high file restoration speed. Both LTO and SDLT technologies use similar-size square, one-reel cassettes with half-inch-wide tape. Smaller, rectangular AIT-3 cassettes use two reels and 8-mm-wide tape.

The LTO standard was created in 1998 by HP, IBM, and Seagate Technology, each of which makes drives that can use any manufacturers LTO cassettes. First-generation LTO cassettes have a raw or native data capacity of 100GB and a compressed capacity of 200GB.

HP started shipping the first drives and automated solutions for second-generation LTO in November 2002. This format has double the capacity—200GB native and 400GB compressed—and provides unparalleled read/write speeds. But attaining these speeds requires a fairly sophisticated network, with high-speed connections between your hardware, and also depends on the types of data being backed up and the speed of the hard drives holding that data.

SDLT 320 is the latest advance in Quantum Corp.s venerable DLT technology. It has the advantage of backward read compatibility, meaning it can read older DLT formats. SDLT 320 has a capacity of 160GB native and 320GB compressed.

Sonys AIT-3 technology has grown in popularity because of its smaller, thinner cassettes, which result in tape libraries that take up a mere 1U of rack space. AIT-3 has a capacity of 100GB native and 260GB compressed. Though it restores files quickly, it performs backup operations much more slowly than the other formats.

The most obvious difference among the formats is how data file locations and other drive-specific information are stored. LTO and AIT-3 cassettes both have on-board chips that store tape-specific information. While the original LTO Ultrium 1 specification allowed data location information to be stored on these chips, none of the manufacturers built this technology into their drives.

LTO and SDLT drives must read the beginning of a tape to determine where files are stored. So far, LTO chips have been used exclusively to store drive-specific information, such as which company manufactured the drive and technical details about proprietary drive functions. But AIT-3 realizes its extraordinarily high restore speeds from the contents information stored on its chips. Each technology has advantages and disadvantages, but during our testing, the relatively similar performances of LTO and SDLT drives proved the differences between them to be negligible.

When selecting a format, remember the bottom line, and not just in terms of hardware. Depending on the format, each tape can cost from $60 (AIT-3) to $100 (LTO and SDLT). IT managers and administrators must keep in mind that depending on their backup schedule, a years worth of media cartridges can end up costing more than the hardware.

Davis D. Janowski Davis D. Janowski is Lead Analyst for Web Applications and Software, charged with covering the likes of Google, Microsoft, Yahoo!, and millions of other Internet and Web companies. Prior to this, he served as Section Editor for Consumer Networking, GPS Products, Phones & PDAs (Mobile and VoIP), Associate Editor for Networking Infrastructure, and Associate Editor for Internet Infrastructure. Before joining PC Magazine, Janowski worked as a medical editor, covering epidemiology and infectious diseases, receiving training at the Centers for Disease Control. At one point, he acted as guide for a CDC team, collecting ticks for a study on the origins of human ehrlichiosis in the Florida bush. Before that he made a very modest living as a freelance writer and photographer, covering scuba diving and nautical archaeology.

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