26 Safeguards Against LAN Data Loss

We test single-medium tape drives for backing up midrange networks--DAT, QIC, 8-mm, and DLT

Tadesse W. Giorgis and John McDonough

NOTE: In the May issue, BYTE published a correction to this article. See http://www.byte.com/art/9505/sec2/art3.htm.

We no longer need to convince people to back up critical data. Now it's a question of how to back up data efficiently. Today's stand-alone systems and network servers, with on-line mass-storage capacities of several gigabytes, require high-capacity backup and archiving subsystems. For many businesses, the primary objective of backing up data is to guard against data loss. In the long run, however, the finite capacity and nonremovable nature of desktop systems' hard drives put secondary storage right up there with death and taxes--it's a must.

Several types of streaming-tape recording media continue to be the backbone of computer backup and archiving for the LAN market. Since the early 1980s, QIC (quarter-inch cartridge) tape drives have dominated secondary-storage solutions for stand-alone systems and LANs. However, QIC drives compete with two other tape technologies from the consumer electronics market: 4-mm DAT (digital audiotape) drives and 8-mm videocassette tape drives.

As storage requirements grow, DLT (digital linear tape), originally developed by DEC for use on midrange and high-end computing systems, is gradually gaining market share in the LAN segment of the industry. Compared to DATs and QIC tapes, DLTs have higher capacities and are faster. Quantum acquired the DLT technology last October, when it purchased DEC's Avastor OEM tape and disk storage business unit.

Based on the videocassette recording technique and using the DDS (digital data storage) specification adva nced by Hewlett-Packard and Sony, DAT technology offers recording capacities ranging from 1 to 5 GB of uncompressed data on a 4-mm minicartridge. The 8-mm helical-scan videocassette tape (presently sourced only by Exabyte) offers from 2 to 5 GB of uncompressed data.

DLT drives can achieve up to 20 GB without compression. We tested systems based on the DEC DLT2000 drives, which can store 20 GB of compressed data; we did not test units based on the higher-capacity DEC DLT4000 drives, which can store up to 40 GB of compressed data.

Rewritable optical drives, WORM optical drives, and rewritable CD-ROMs (see ``CD-R Backup Systems Compete with Tape'') are also alternatives for secondary storage.

We tested 26 tape-backup subsystems ranging in capacity from 4 to 10 GB native format (i.e., without compression). Their prices range from the truly affordable Sony SDT-5000 internal DAT drive to the high-priced CTS-2110 DLT drive from TTI.

HOW TO USE THIS GUIDE

To find th e right tape-backup device for your needs, follow the main headings until you come to the appropriate category. Then look for the subsystem that is most relevant to your network environment and specific backup and archival needs.

The tested tape-backup devices are grouped first by configuration (e.g., server-attached or workstation-attached) and by technology: 4-mm DATs, 8-mm helical-scan tape subsystems, half-inch DLT drives, and QIC drives.

The features score rates how well the tape-drive subsystem is adaptable to a particular computing environment, including hardware platform support, backup software support, and desktop and NOS (network operating system) compatibility.

Ratings for overall winners from each category are picked by taking a weighted average of the backup and restore performance score (75 percent), the features score (15 percent), and the usability score (10 percent). Using a scale of 1 to 10, 10 is best.

This rates how well the documentation simplifies installation an d use of the tape drive.

Price as configured; typically, the cost varies based on the bundled software and the interface hardware.

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The Inside Story

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THE INSIDE STORY

CASSETTE
DATs were developed for audio recording. DAT tapes are 4 mm wide and can pack data more densely than many types of computer media.

CAPSTAN AND MOTOR
A capstan is a vertical rotating shaft that drives tape at a constant speed. The capstan and the drive belt control tape speed and avoid speed variations caused by overrunning and underrunning, the biggest factor in a tape's demise.

HEAD CLEANER
DAT drives include an internal head cleaner, but you should use a cleaning cartridge regularly as well. Intelligent backup software will tell you when it's time to clean the heads.

LOADING GEARS
Gears on both sides of tape drives both pull in and eject the tapes.

ID JUMPERS
You may need to set the ID jumpers to comply with your tape drive's SCSI ID address.

DRUM ASSEMBLY
In helical-scan systems (DATs and 8-mm drives), the rotating heads are mounted on the drum. When in use, two arms pull the tape out of the cartridge and wrap it partway around the drum.

SCSI INTERFACE
All the tape drives in this review support SCSI-2. Some of them include LEDs to show proper SCSI termination.

RF BOARD
The RF board picks up the RF signal that's stored on the tape recording and converts it to digital signals.