What's the worst thing that can happen to your computer?

Worse than a hard disk crash, virus infection, spam assault, denial-of-service attack, hacker takeover, fire, flood, or other human, mechanical, or natural disaster is a faulty backup when you really need it. If the computer blows up, you can recover as long as your data is backed up securely.

Tape backup is still popular among business users because of its long use and cost-effectiveness per megabyte of data.

This is despite the increasing popularity of other backup solutions. Many home and small businesses use recordable CDs and DVDs to back up newly created data. Various types of computer users are now employing an external hard drive, connected to a USB port, to quickly and cost-effectively back up entire hard drives. Those with broadband Internet connections can use Internet backup services to conveniently store selected backup data off-site.

Still, tape backup has a large installed base. But like anything having to do with a computer, backing up to tape isn't foolproof. Tape drives, backup tapes, and tape backup software can fail.

When they do, panicked computer users often rely on the services of a data recovery firm such as CBL Data Recovery Technologies Inc., a company headquartered in Armonk, N.Y., with branch offices around the world and a Web site at http://www.cbltech.com.

CBL and companies like it want your business, and they try to be helpful in multiple ways. Here's how you can minimize the chances of a tape backup failing in the first place, according to Doug Owens, managing director of CBL's San Diego laboratory and resident tape expert. Many of these same precautions apply to other backup systems as well.

Make sure you have more than one copy of a backup tape. Instead of using the same tape time after time, use multiple tapes, rotating through them. You can use any of a number of different systems for this.

With the odd/even system, you use one tape on one day, a second tape the next day, reuse the first tape on day three, and so on. With the 5-day rotation system, you use a different tape for each day of the week.

Backup tapes are typically rated to be used from 5,000 to a half million times, depending on the type of tape. Tape backup software typically will keep track of the tapes, regardless of the rotation system you go with.

Make sure you verify your backups. Most backup software will automatically do a quick "read-after-write" verification and will optionally do a full verification. The latter is more thorough and more time-consuming, roughly doubling the backup time.

If your data is crucial, it can make sense to do a full verification on a regular basis.

Make sure your equipment is being maintained properly. You should clean your tape backup drive periodically, following the directions in its manual regarding frequency.

You also should consider having an authorized maintenance person from the manufacturer of the tape backup drive or from a third-party repair firm check the alignment of the drive every 12 to 18 months. Most businesses just send the drive back to the manufacturer when it begins to have problems, but if a drive has problems, so can the backup tapes.

Make sure you store one backup tape off-site. This will ensure that your data is preserved if your site experiences a fire, flood, earthquake, hurricane, tornado, volcanic eruption, or other disaster.

Some companies swap backup tapes with other offices (for example, sending them via Fed Ex). Others periodically do a "remote backup" through the Internet from one office to another. With some small businesses, a selected employee takes the backup tape home with him. A further option is using an off-site storage firm, which provides fire-protected storage facilities for print and digital media as well as tape.

Make sure that the backup tapes kept on-site are stored in a stable environment without exposure to extremes in temperature, humidity, or electromagnetism. Don't, for instance, store the tapes in a safe on the opposite side of the wall from a large generator, whose electrical fields can wreck havoc with the data on them.

Finally, make sure you periodically test your backup tapes and your restore procedures. You can, for instance, try restoring some of the data on the tapes to a different server or to a different partition or folder on the same server where the original data is stored.

With backups, the old maxim applies: Better safe than sorry.