- Backups must be recent to be useful. The older the data is, the more you have to replace to get up to date after restoring from the backup

- Backups must be reliable. You must be able to actually restore data from the backup for it to be of any use. e.g. have you stored the backup software so you can actually access your Zip disk/CD-ROM/QIC drive? Hmmm? Think about it! If the computer crashed and your only copy of the backup software is on the dead hard disk, how will you read your backup?

- Backups must not be overwritten too soon. You don't want to re-use a recent tape only to discover you just wiped out the only good copy of your data.

There are two types of backup: incremental and full. An incremental backup only saves the data that has changed since the last backup. This means that much less data needs to be saved and it is much quicker. A full backup, as its name suggests, copies everything, whether it has changed or not.

Typically, a good backup scheme can goes like this 'Grandfather-Father-Son' rotation scheme. This scheme uses daily (Son), weekly (Father), and monthly (Grandfather) backup sets.

- Monday - incremental backup to tape 1
- Tuesday - incremental backup to tape 2
- Wednesday - incremental backup to tape 3
- Thursday - incremental backup to tape 4
- Friday - full backup to tape 5. This is called Week 1 Backup.

So, if disaster struck on a Wednesday, you would do a full restore from the previous Friday's weekly backup tape and then restore the updates from Monday's and Tuesday's tapes.

The next Monday you would re-use tape 1 for an incremental backup.
Next Tuesday, use re-use tape 2.
Same for Wednesday and Thursday - use tapes 3 and 4 again.
Next Friday, do another full backup to Week 2 backup (tape #6).

This way, if you discovered corrupt data a week after it happened, you could still recover data way back from week 1.

Week 3 is the same as week 2, using Week 3 backup (tape #7) on Friday.

At the end of the fourth week, do a full backup to Month 1 backup tape (tape #8).

At the end of the fifth week, Week 1 tape is re-used.

Can you see the pattern? The daily tapes are recycled weekly. The weekly tapes are recycled monthly. Monthly tapes are recycled annually. Of course each year a full annual backup is kept safely stored and never re-used.

Naturally, you can see the daily tapes (tapes 1-4) are used much more often than the weeklies and monthlies. This will mean they will suffer more wear and tear and may fail more readily because they are getting old. What happens is that the tapes that are used most get "promoted" after a time. A tape (e.g. tape 1) will be used as a Weekly tape after, say, a month of daily use. After a year of weekly use it can be error-checked (in case it's getting unreliable) and "promoted" to become a Monthly tape. After 12 months it could be "retired" and spend the rest of its days relaxing on a shelf as a permanent Annual backup tape, complaining about the disgraceful behaviour of young backup tapes nowadays.

Annual backup tapes should be duplicated, just in case the original fails, since this is the only surviving copy of this data.

This scheme is sometimes known as the Child/Parent/Grandparent scheme because a brand new young tape starts being active and vigorous, in middle age it slows down its hectic life to only work once a week, and in old age it takes a final recording, puts on its slippers and sits on the porch enjoying itself.

A well-managed backup procedure is required. An organisation must have a rigid set of procedures that determines who is in charge of backups, when it is done, how it is done. A slapdash approach will inevitably lead to bungled backups.

Your backup isn't successful until you've managed to recover data from the backup. Make sure you occasionally do a restore test to ensure that you can, in fact, recover data from your backups. If you can't, you're wasting your time doing backups!

Backups must be stored offsite. Storing the backups in the company's building is futile if the building burns down. Typically, the backups are taken home by a reliable person or stored in a safe place (such as a fireproof safe). Paranoid managers may make copies of backup tapes and store them in two separate places. Of course if the data is really secret and sensitive, the more copies you make, the more danger there is of data being lost or stolen.