Demystification Of Tape Technologies.

A decade ago the choices for network backup were simple. Quarter-inch, 8mm, and 4mm were the primary options for high capacity backup. Today this situation is dramatically different. Multiple choices in both linear and helical scan formats offer users more freedom to choose the tape option that best meets their requirements, from small offices to departmental and workgroup environments to multi-terabyte enterprise applications. Driven by an explosion in storage growth worldwide, tape automation has emerged as one of the hottest markets in the industry, with International Data Corp. projecting tape automation sales growing at an annual rate of 25 percent, creating a market opportunity of more than $5 billion by 2003.

Never have users had the range of tape automation options available today, with new formats scheduled for arrival later this year. Overland operates with a "format neutral" approach to the needs of its customers. The company's tape automation solutions accommodate a range of tape formats to take advantage of whichever tape technology best meets customer requirements. Today Overland offers solutions incorporating DLT, DLT1, SDLT, AIT, LTO Ultrium, SLR, 4mm, 36-track, and Travan NS technologies.

Traditionally, tape technology has been categorized by the drive recording method: linear, with Quantum's DLT currently the leading format, or helical scan, consisting of 4mm DAT, Exabyte's Mammoth, and Sony's AIT products.

This piece provides an overview of each of the tape technologies within the linear and helical recording methods, as well as highlights of Overland's offerings.

Linear Tape Overview

Linear tape technology utilizes a recording method in which the data tracks are written in a linear pattern on the tape. The first set of tracks are recorded in parallel the entire length of the tape. The recording heads are then repositioned and the tape direction is reversed to record the next set of tracks, again across the entire length of the tape, repeating this process until all data has been recorded.

Another key feature of linear tape technology is the boost that certain formats have received from Overland's patented Variable Rate Randomizer (VR2) technology. VR2 is the first successful implementation of Partial Response Maximum Likelihood (PRML) channel encoding technology on linear tape drive platforms, and improves code rate efficiency of linear tape drives to more than 99%. The efficiency of its high code rate increases the native capacity and native data transfer rate performance of existing linear tape technologies by 50% to 100% without requiring any changes in tape path design, recording heads, and/or media. To date, Imation, Seagate, StorageTek, and Tandberg Data have all licensed VR2 technology for incorporation into their own linear products; Imation and Seagate for their Travan products, Tandberg with its SLR line, and StorageTek with its high-performance 9840 product.

DLT/SDLT

Quantum's DLT technology has carved out a position as the preferred tape format for mid-range and high-end .backup applications with more than 1.4 million drives installed to date. The appeal of DLT is based on its high capacity combined with its high performance and proven durability. DLT 8000 is Quantum's current top of the DLT line. With a native capacity of 40GB and a sustained data rate of 6MB/sec, DLT 8000 is an interim step on the way to SuperDLT, and is fully backward read compatible with the installed base of DLT 7000 and DLT 4000 tapes.

Quantum's next generation DLT product is SuperDLT. SuperDLT delivers a major step up in capacity and performance. First generation SuperDLT drives offer a native capacity of 110GB per cartridge and a data transfer rate of 11MB/sec, while still providing the option for backward compatibility with DLT 4000, 7000, and 8000 products. Quantum has laid out a multi-generational migration path for SuperDLT technology that will produce drives with 1 TB of capacity and data transfer rates of 100MB/sec.

Overland currently offers DLT-based automation solutions with its scalable, multiterabyte LibraryXpress and EnterpriseXpress, affordable MinilibraryXpress, and entry-level LoaderXpress. Overland has recently commenced shipping SDLT versions of the MinilibraryXpress and LoaderXpress with SDLT versions of other existing products to follow. Overland will offer next-generation automated DLT solutions with DLT 8000 and SDLT, in keeping with the company's strategy to offer the widest variety of DLT technologies.

DLTI 

While DLT has dominated the mid-range tape market for the past decade, the drives have been relatively expensive for entry-level applications. That issue has been addressed by Benchmark Storage Innovations with its DLT1 products. DLT1--designed by Benchmark and utilizing fundamental DLT technology licensed from Quantum--delivers the benefits of DLT technology at a fraction of the price. Benchmark's first product, the DLT1 drive, offers the same native capacity as DLT 8000 (40GB per cartridge) and a transfer rate of 3MB/sec for less than half the price of a DLT 8000 drive.

Overland offers two DLT1 solutions: a DLTl tape drive subsystem and a LoaderXpress ten-cartridge autoloader with DLT1 technology.

Linear Tape Open

Linear Tape Open (LTO) is the newest linear tape format on the market, the result of a consortium between Hewlett-Packard, IBM, and Seagate Technology to create a high-performance open tape standard available for licensing to any interested parties. LTO consists of two formats: a high-capacity format designated Ultrium and the Accelis fast-access design. The two formats use different physical tape cartridges and are not compatible.

The LTO Ultrium format has garnered most of the attention as an alternative to SuperDLT. Ultrium provides a native capacity of 100GB per cartridge and up to 16MB/sec data rate. Among the innovations in the LTO Ultrium format is a Cartridge Memory feature, similar to Sony's Memory-in-Cassette technology that allows immediate access to the tape's file directory information.

Overland has announced an agreement with Seagate for LTO Ultrium technology under which Seagate supplies Overland with its new Viper 200 drives, based on the LTO Ultrium format, for incorporation into Overland's LoaderXpress. In turn, Overland provides a version of the LoaderXpress to Seagate, which Seagate will market as the Viper 2000 Autoloader. Overland recently began shipping its LTO Ultrium LoaderXpress and will offer next-generation automated solutions with the Ultrium format in the near future.

Travan NS

The Travan format was originally developed by Imation and is licensed to other manufacturers, including Seagate and Overland's Tecmar subsidiary. Travan NS (Network Series) is a value leader in tape technology for small office and entry-level server backup applications. Travan NS20 drives--the current state of the Travan art--are available for less than $600. For that price customers receive a drive with 10GB of native capacity and 1MB/sec data rate performance, along with features usually limited to more expensive solutions, such as read-while-write data verification. The next generation is scheduled to arrive from Tecmar in the second quarter of next year. The key enabling technology for this breakthrough is the incorporation of Overland's VR2 encoding technology.

Helical Scan Overview

Helical Scan tape drives are based on a recording method in which data tracks are written at an angle with respect to the edge of the tape. This recording method delivers very high-density storage on small format tapes. While linear recording moves the tape at very high speeds across a stationary recording head, helical drives utilize n slow moving tape and high-speed rotating drum containing the recording heads. While data rate performance is typically a function of the tape speed, helical recording produces effective tape-to-head speeds similar to linear recording, enabling acceptable data rates. The major helical formats for data recording include 4mm DAT (DDS) which Overland's Tecmar division sells under the WangDAT brand, and 8mm, consisting of Exabyte's Mammoth products and Sony's AIT (Advanced Intelligent Tape).

Jim Jenkins is the director of product marketing at Overland Data, Inc. (San Diego, CA).