tape storage

Exabyte VXA-2 Tape Backup System

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By Joel Shore

May 3, 2003

It goes without saying: If you are a network administrator, you’ve already developed a comprehensive plan for backing up the data on your servers. Right? If you haven’t done this yet, put it on your calendar for today—not tomorrow, today. Today!

One thing we all know is that disk-storage prices have dropped like a rock even as capacity has skyrocketed. Like moving into a bigger house, these giant disk drives have more room for more stuff. That means more files to back up. And that means using tape drives. Big tape drives.

As the years passed and the need for high-capacity tape storage grew, various technologies have come and gone. The alphabet soup of these technologies, QIC, DLT, DDS, and others have given way, at Exabyte, to VXA. The format clearly is a winner: Apple, Compaq, Fujitsu, IBM, Logitech, and Toshiba have all signed on. Expect more to follow.

Key advantages. DDS-4 tape drives, among the most common in use today, just can’t compete anymore. The maximum capacity of a DDS-4 tape drive, with data compression, is only 40GB, a mere pittance by today’s standards. After all, you can buy an entire computer, complete with 80GB-drive, for less than $1,000. VXA-2 drives are huge in comparison—they hold four times as much. With compression, you’ll fit up to 160GB of data per cartridge.

Not only does VXA-2 boost capacity by a factor of four, it’s also twice as fast as DDS-4. Combine that with hardware that’s less finicky, and you wind up with, well, bigger, faster, and more reliable. That’s a darn compelling argument.

Finally, to make matters even worse for intrepid DDS users, the manufacturers of tape drives have chosen to abandon DDS altogether; DDS-5 will never see the light of day. That makes the DDS format a lame duck. Thinking of migrating from an old, slow, small DDS-4 drive? Think VXA-2.

I took a look at Exabyte’s external VXA-2 tape drive, which provides 160GB of data storage through a low-voltage differential (LVD) SCSI connection on a single tape cartridge. If your backup needs are greater, VXA-2 is also available in either 7-tape or 10-tape multicartridge autoloaders. You can get capacity up to a whopping 1.98TB (that’s terabytes, nearly two trillion bytes!). Exabyte also manufacturers a VXA-2 drive with a FireWire interface.

VXA is different. Packets and variable speed make VXA different from other tape technologies. Older technologies recorded by placing data in a continuous stream, parallel to the edges of the tape. Called linear recording, it’s very similar to the way audio cassette tapes work. Linear recording eventually gave way to the more-modern helical-scan recording scheme in which a spinning recording head laid down tightly packed data tracks at an angle to the tape’s edges, just like the VCR sitting next to your TV. Like linear recording, helical-scan recording looks at the data as a continuous stream.

VXA takes those long data streams (a large file, for example) and splits them into small chunks, called packets. It’s very similar to the way your network breaks down a large file into packets for transmission over the Internet. As each packet is written to the tape, it is verified for integrity. The intent is to ensure complete reliability.

Also unique to VXA is VSO, Variable Speed Operation. VSO enables VXA drives to adjust the tape speed to match the data-transfer rate of the computer furnishing the data. How cool is that? This on-the-fly speed adjustment enables VXA to eliminate productivity-reducing back-and-forth tape movement (“backhitching”) and wear and tear (on both the tape and the drive). The aim, again, is better performance, greater reliability, and absolute data integrity.

Simple Installation. Setting up a VXA-2 drive is rather straightforward. First, you’ll need a SCSI adapter installed in the host computer or server. The drive does not include a data cable, so be sure to have a Wide LVD, 68-pin cable on hand. The external version of the drive includes a terminator, the internal version does not.

As with any SCSI device, you first set the SCSI ID by pressing the “+” or “—” tabs on the SCSI ID switch. Next, you connect the SCSI cable from the computer to either of the SCSI ports on the tape drive’s rear panel. If you have several SCSI device connected in the chain, and the drive is the last one in the chain, install the terminator on the unused port. Finally, connect the power cable.

When you power up the drive, its four LED indicators flash in sequence, letting you know that it is doing a self-test. When this diagnostic routine is completed, the power indicator LED illuminates in solid green. Next, you load a tape and wait for the tape indicator to light up in solid green. The drive is now ready for use.

Before you can make backups, you’ll need to configure your backup software to recognize the presence of the VXA-2 drive. Once this is done, be sure to run a small backup and restore test to make sure everything is configured and working properly. After you’re satisfied with the test, you can place the drive in service.

Why run a complete backup-and-restore test? Simple. No one really cares if a drive can record data. It’s retrieving it that counts!

Exabyte’s VXA-2 tape drive is fast, reliable, and offers oodles of capacity on a single tape cartridge. For new installations, it’s a great way to go. And when the time comes to retire your DDS-based drives, VXA-2 is hard to beat. <