Setting up a backup system is an essential task for any business, but it can also seem a complicated process as a full-proof system relies upon more than one technique. That way the weaknesses of one backup system can be offset by the complementary strengths of another.

A RAID (redundant array of independent or inexpensive drives) setup of internal hard drives can update a data backup in a split second. Unfortunately, it does not safeguard against the accidental deletion of data or the total destruction of a computer.

In this feature I'll look at backups that use removable storage media and discuss backup rotation and off-site storage.

Backups involving removable storage media are more time-consuming to perform than using RAID, taking up to several hours. However, daily backups can help recover accidentally deleted files that are more than a day old. And off-site storage of your backup media protects against a major disaster such as a fire, flood, or theft.

What's the best removable storage?

Let's consider the types of removable storage media available for your backup. Ideally, you want a relatively inexpensive form of data storage that is durable and reusable. It should have sufficiently high capacity to store all or most of your critical business data on one unit of media. The storage medium should be widely available and commonly used, so that the data on it can be quickly accessed and restored on another computer should the original PC be destroyed.

These requirements rule out some types of removable media fairly quickly. For example, while the floppy disk was once a favourite for backups, its limited storage capacity makes it virtually useless today. Most new PCs don't come with a floppy drive, so it's not even the universal portable storage solution it once was.

Optical discs

There was a time when I recommended CD-R media for backups. However, most businesses - except for one-man-bands or recently established firms - will have a greater quantity of important data than the 700MB or so that can be stored on a single CD.

Of course, you can spread a backup over multiple CDs, but shuffling discs in and out of drives isn't convenient, nor can it be easily automated using a standard CD drive.

Optical disc jukeboxes can shuffle 100 or so discs. But optical jukeboxes aren't cheap, and replacing discs for each new backup set could be time consuming.

Recordable DVDs - which provide 4.7GB of storage on single-layer discs, 9GB on dual-layer discs - can be a good solution for many small businesses. The discs are so inexpensive you needn't be concerned about reusing the media. (See an article on our US sister title PC World's site discussing archival-quality DVDs.)

The latest members of the optical media family - Blu-ray Discs and HD DVDs - can store even more data, up to 50GB per disc for Blu-ray and about 30GB for HD DVD. The blue-laser burners needed for these media are relatively expensive today, but will be more affordable in a year or two.

Flash memory and tape

USB sticks (sometimes called thumb drives) loaded with non-volatile flash memory can be another good backup choice, with prices dropping considerably over the past year. A couple of my clients prefer using flash memory drives for document backups because they're so small and convenient to transport.

Tape cartridges are yet another option. I'm no longer as big a fan as I once was of tape, despite the low cost per gigabyte, large storage capacity, and durability of the medium. I have two principal concerns.

First, there are more than a dozen different tape formats. Tape cartridges that appear physically similar can store data in incompatible formats. This can make recovering data quickly at an alternate work site difficult.

Second, tape is a sequential-access medium, as opposed to the random-access nature of most storage alternatives. Random-access means the PC can move directly to where the data is stored on the media, with near instantaneous access, as with a hard drive. Sequential access means the PC must always start at the beginning of the media, then advance in sequence until the data is located on the tape.

With sequential media, recovering deleted email messages sent or received over a period of several months from daily backups could take hours: You must wait while each tape slowly winds its way to the required data. Think you'd never need to do this? Wait until your business gets hit with litigation that demands discovery of electronic documents.

External hard drives

Hard drives can be excellent storage media for backups, since they're fast and high in storage capacity. Some vendors offer external hard drives that you can plug into your PC or server; these products are perfect for backups. Some external drives come bundled with backup software; you simply push a button on the drive to start the backup.

External drives with a USB 2.0, Firewire, or eSATA connection will be fast enough to keep backup times manageable.

There's also a class of products called network-attached storage devices for greater backup needs.

My picks

For businesses with up to 8GB or so of important data, either a USB stick or DVD burner would work well; DVDs make it easy and inexpensive to maintain backups made over time.

I suggest that businesses with greater storage requirements use external hard drives.

Backup rotation

Periodic rotation and transport of back-up media to off-site storage will protect against theft or loss due to destruction of the premises.

I recommend maintaining a minimum of three backup generations. Backup A can be attached to the computer or network. Backup B can be stored securely on premises. Backup C should be stored safely off-site. Then rotate the backups, taking backup B off-site, attaching backup C to the computer, and moving A elsewhere in the office.

A small owner-managed business may opt to store the off-site backup at the owner's home; an alternative is to rent a box in a bank vault. Larger businesses with multiple locations may swap backups between sites. Some small businesses may make similar swap arrangements.

If you use a courier or other common carrier to transport your backup to another location, I strongly recommend that you encrypt the data. If the backup is lost or falls into the wrong hands en route, encryption will help ensure that confidential business data remains confidential.