Feature

Cutting through the tape maze

Ezine

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Mammoth-2 8mm tape systems provide an average 60-second file access, high-density tape recording (up to 150GB, compressed) and reliable (50,000-hour head life; 20,000 tape passes) backup for large-scale network servers requiring storage of large volumes of images and data. Mammoth drives provide a 30MB/s (compressed) data transfer rate at a media cost of approximately $92/cartridge or $0.61/GB.

Mammoth supports the same Advanced Metal Evaporated (AME) media as AIT, and, therefore, has the identical archival rating. Exabyte's drives come in a 5.25-inch, half-height footprint and offer a Fibre Channel (FC) interface as well as support for all versions of SCSI. This technology is compatible with Unix, Linux and NT environments.

What's in store for 8mm? AIT-3, which began shipping last January, is the first of four planned generations (AIT-4, AIT-5 and AIT-6). Sony is committed to doubling capacity and transfer rates every 18 months, with the AIT-6 reaching 800GB (native), 96MB/s (native).

Sony is also working on a new family of drives (S-AIT) slated for introduction at the end of this year. The first generation will have a 500GB capacity (native) with a 30MB/s (native) throughput rate. The S-AIT road map calls for four generations, reaching a native capacity of 4TB.

Mammoth-3 from Exabyte is ready to begin shipping. It has a 120GB capacity (native) and a transfer rate of 14MB/s (native). A new super drive that combines Mammoth and

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VXA tape technology is also under development and is expected to be released in an 18-month time frame. Capacities and transfer rates have not yet been finalized.

Digital Linear Tape
Digital Linear Tape (DLT) technology has been a leader in high-end tape backup for many years. These tape devices are suited for situations where the backup window is small and the amount of data to be backed up continues to grow. The new Super DLT (SDLT) tape targets the high-end midrange systems, network servers and mainframe backup and archiving markets. DLT tape technology has been around since the 1980s and has proven to be rugged and dependable in full-duty cycle environments. It's easy to integrate, reliable enough for the most demanding applications and SDLT is backward compatible with previous DLT generations.


DLT highlights
DLT CAPACITY
(COMP)
TRANSFER
RATE
FORM
FACTOR
APPROX.
PRICE
SDLT 220 220GB 22MB 5.25" $4,000
SDLT 320* 320GB 32MB 5.25" N/A
*due for release later this year
DLT drives are manufactured by Quantum Corp. DLT products support most of the popular operating systems and interface with all SCSI buses. The drives are available in the 5.25-inch form factor.

DLT technology is a modern adaptation of the old reel-to-reel tape methodology where the tape cartridge performs as the source reel and the tape drive as the take-up reel. The tape is guided, not pulled, past a stationary head, in contrast to helical scan's spinning head and pulling technique. The recorded side of the tape never touches the guides, minimizing tape wear. The drive utilizes 1/2" tape (this is 60% wider than 8mm tape) and records by writing data in a serpentine pattern on parallel tracks. Each track spans the entire length of the tape. When the end of the tape is reached, the heads are repositioned to record a new set of tracks and recording again continues over the entire length, this time in the opposite direction.

The current generation of Super DLT drives, (SDLT 220), provides 70 second file access, storage capacity of 220GB (compressed) with an estimated shelf life of 30 years and a 30,000 hour head life, with a rating of 1,000,000 tape passes. SuperDLT drives are capable of data transfer rates up to 22MB/s (compressed).

However, having a fast tape drive doesn't ensure the highest throughput. If the transfer rate of a tape drive is faster than the host data rate, the tape must stop and reposition frequently, degrading performance. DLT technology incorporates a feature called adaptive cache buffering to achieve maximum throughput. The drive monitors the host system and dynamically adjusts the cache buffering operations to match the host data rate, thus minimizing delays due to repositioning.

What's in store for DLT? Quantum's latest road map starts with the SDLT 320 expected out later this year. There will be four generations of SDLT drives, with a new product introduction every 18 months. Each generation will double capacity and transfer rates until topping out at 1.2TB (native), 100+ MB/s (native).

Linear Tape Open
Linear Tape Open (LTO), developed by a consortium of IBM, Seagate, and Hewlett-Packard, is an attempt to break the proprietary hold Quantum has on high-capacity linear tape and to offer an open standard alternative. LTO formats employ a multichannel linear serpentine recording method similar to DLT (data is recorded in tracks that run down the length of the tape; the tape makes multiple passes past the read/write heads from one end to the other and then reverses direction).


LTO highlights
LTO CAPACITY
(COMP)
TRANSFER
RATE
FORM
FACTOR
APPROX.
PRICE*
Accelis 50GB 20-40MB 5.25" N/A
Ultrium 200GB 20-40MB 5.25" $5,000
*Seagate 200 LTO Ultrium; other vendor prices vary.
This technology builds on the success of linear tape formats with advances in servo technology, data compression and error correction coding. LTO supports two formats - Accelis and Ultrium. Accelis is in development and will be designed for applications requiring exceptionally fast access times, such as libraries used in online data inquiry and data mining applications; it can deliver transfer rates up to 40MB/s (compressed). The Ultrium format is aimed at users who require high-capacity backup, restores and archive applications. It is capable of supporting LTO cartridges of varying capacities up to 200GB (compressed).

LTO Accelis utilizes a two-reel, self-contained 8mm cartridge. The cartridge loads with equal amounts of tape on each reel, minimizing access times. Accelis will serve automated environments needing tape storage solutions for a wide range of online data inquiry and read-intensive applications.

LTO Ultrium cartridges are of a single-reel design and utilize half-inch tape media. Tape is extracted from the cartridge by the drive and wound onto a take-up reel contained within the drive itself. Ultrium is suited for backup, restore and archive applications in either standalone or automated environments.

This was first published in July 2002

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