Tape technology is broken into two major categories: helical tape and linear tape. The former touts higher density and performance, while the latter promises increased reliability. The main difference between the two is that a helical-scan drive pulls the tape out of the cartridge and, using a series of tensioners, wraps the tape around a rotating drum that contains the heads. Linear scan uses stationary heads and a less complex tape-threading method. The stationary heads of the linear tape technology are what theoretically give linear-tape drives superior reliability.

The other difference is the way data is written to the tape. Linear scan writes data from front to back in a serpentine method. That is, when the head reaches the end of the tape, it drops down a row and switches direction. Helical scan writes data diagonally across the entire tape--simultaneously using multiple heads. Concerns about the tape stretching or snapping due to drum rotation speeds upward of 7,000 rpm and high tension conditions have been quelled by the success and reliability of solutions such as the Sony AIT-2 drive. Aided by DLT, linear-scan drives have been winning the race with proven market success.

Enterprise Tape Drives

Quantum DLT 8000

It seems fitting that we first examine what is known as the "king of the tape market," the DLT. As the name implies, the DLT is a linear- tape technology. The new DLT 8000 supersedes the popular DLT 7000 and the aging DLT 4000. Although the DLT 8000 is a new drive, it features only modest improvements over the DLT 7000. With a native capacity of 40 GB, up from 35 GB, and a native transfer rate of 6 MBps, up from 5 MBps, the DLT 8000 isn't exactly breaking new ground. Those numbers double, however, when we take into consideration the theoretical 2:1 hardware compression ratio performed by the drive.

Performance doesn't tell the whole story. The DLT 8000 was designed for heavy use in the enterprise to back up mission-critical data automatically. With such importance put on data integrity, Quantum Corp. has beefed up the DLT 8000's reliability. With an increased MTBF (mean time between failure) of 250,000 hours, up from 200,000, and nearly double the head life at 50,000 hours, up from 30,000, DLT is poised to maintain its market position. These numbers are based on a 100 percent duty cycle, whereas some drives base their stats on as little as 10 percent duty cycles.

Another advantage of the DLT 8000 is its backward compatibility with previous-generation DLT drives. Because those who already have archives of DLT tapes may be reluctant to migrate from DLT, the DLT 8000 offers an excellent path to upgrade from DLT 4000 or to add a new tape library. The DLT 8000 has an expectable price point for an enterprise-class drive; a bare drive costs around $5,000.

Exabyte Mammoth-2

Attempting to dethrone the DLT in the enterprise, Exabyte has significantly revised the Mammoth drive, dubbing it the Mammoth-2. In a case of "too little, too late," the original Mammoth offered reliability but fell short on price and performance. With the new Mammoth-2 drive, Exabyte has delivered a very capable enterprise-class tape drive. Exabyte is also positioning the Mammoth-2 for the backup-automation market. Exabyte has its work cut out, however, with the Mammoth-2. Unlike DLT, the Mammoth-2 uses helical-scan technology, which remains an unproven technology in the enterprise arena, though AIT-2 is helping to change that. Moreover, administrators are gradually rebuilding their confidence in Exabyte.

Regardless, the numbers for the Mammoth-2 are impressive. With a native capacity of 60 GB, up to 150 GB compressed, and a native transfer rate of 12 MBps, up to 30 MBps compressed, the Mammoth-2 offers almost twice the performance and capacity of the DLT 8000. Exabyte claims an MTBF of more than 300,000 hours. Also, the Mammoth-2 offers a head life of 50,000 hours at 100 percent duty cycle.

As those who have worked with helical-scan drives know, keeping the heads cleaned is crucial. Exabyte has cleverly addressed this issue with its new SmartClean cartridges. With a small portion of tape cleaner on every cartridge, the drive can clean its heads without user intervention.

In an attempt to remain competitive, Exabyte has kept the price of Mammoth-2 drives down relative to the DLT 8000 drives. It's possible to find single drives for less than $4,000.

Linear Tape Open

LTO (Linear Tape Open) drives have just begun to hit the market. LTO is a new technology jointly developed by Hewlett-Packard Co., IBM Corp. and Seagate Technology, which tried to develop an "open" standard for tape formats. LTO, based on linear tape technology, strives to combine the latest in ECC (error-correcting code) data distribution, data compression and head technology to form a standard that will be the foundation of future tape drives. LTO comprises two separate standards, the Accelis and Ultrium. The former focuses on fast data access; the latter, on higher capacity. When this was written, there was still little known about the actual capacity and performance specifications of LTO.

However, Seagate is releasing the Viper 200, which is based on the Ultrium format of LTO. The performance and capacity of the new Ultrium drive look extremely promising. The Viper features a native capacity of 100 GB, 200 GB compressed, and a native sustained transfer rate of 16 MBps, or 32 MBps compressed. These numbers far exceed anything the market has previously offered. Accelis-based drives are expected to debut with 25 GB of native capacity with native transfers rates around 20 MBps. Prices for Ultrium or Accelis drives have not yet been determined.

Super DLTtape

Quantum, which has been a driving force in the DLT market, has taken up arms against the LTO threat with its new Super DLTtape technology. Leveraging its already successful line of DLT drives, Quantum is also integrating a new LGMR (laser-guided magnetic recording) technology. This LGMR will use a combination of optical- and magnetic-head technologies to produce better performance, higher capacity and more resilient drives than those previously seen in Quantum's DLT drives.

As little as is known about LTO, even less is known about Super DLTtape. Quantum plans to release the Super DLTtape with a native capacity starting at 100 GB and transfer rates of 10 MBps to 40 MBps. These initial statistics would position the Super DLTtape favorably against LTO. Prices for Super DLTtape drives have not been announced.

Sony AIT-2

Following its original AIT (Advanced Intelligent Tape) drive, Sony has released the next incarnation, called AIT-2. Like the Mammoth-2 and DAT (digital audio tape) drives, AIT uses a helical-scan technology to read and write to tape. Sony originally positioned the AIT-2 in the midrange tape market; according to the Gartner Group, however, AIT has become one of the more popular alternatives to DLT. Originally found predominately as standalone drives, AIT drives are increasingly used in tape automation. In fact, Sony has done such a solid job with its AIT technology, it has rolled out some of the highest-capacity tape silo installations in the industry.

AIT tape drives are known for their unique MIC (Memory in Cassette) feature, which acts as a data index. By using MIC, Sony has been able to reduce load times. The new AIT-2 drive features 50 GB of native capacity, 100 GB compressed, with a native transfer rate of 6 MBps, equaling that of the DLT 8000 drive. One detail of the AIT-2 drive to note: It wasn't designed for extensive backup thrashing. The MTBF on the AIT-2 is rated at 300,000 hours but is calculated based on a 60 percent duty cycle. However, the reliability of AIT has been stellar, making the duty cycle a moot issue. Those looking at DLT automation solutions should also be examining AIT-2 as a worthy alternative.

With the high capacity and high speed comes a higher price. AIT-2 drives sell for around $4,000.