Understanding Backup Types and Strategies

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The Backup program supports five common backup types: normal, incremental, differential, copy, and daily.

  • A normal backup copies all selected files to the backup medium, regardless of when the files were last changed, and clears the archive attribute for each file to mark it as backed up.
  • An incremental backup copies only selected files that have changed since the most recent normal or incremental backup, and clears the archive attribute for each file. Therefore, the first incremental backup after a normal backup copies all files that have changed since the normal backup, the second incremental backup copies only those files that have changed since the first incremental backup, and so on.
  • A differential backup copies only those selected files that have changed since the most recent normal or incremental backup. Unlike incremental backups, however, a differential backup doesn't clear the archive attributes for the files it copies. Therefore, successive differential backups copy all the files that have changed since the last normal (or incremental) backup, not just the ones that have changed since the last differential backup.
  • A copy backup copies all selected files, like a normal backup, but it doesn't clear the archive attribute. Therefore, you can use it to perform a special backup (before installing new software, for example) without affecting your normal backup routine.
  • A daily backup copies all selected files that changed on the day the backup is done. It doesn't clear the archive attribute. You can use daily backups to save your day's work without affecting your normal backup routine.

Selecting a backup type involves evaluating tradeoffs between safety on the one hand, and time and media space on the other. If safety were your only concern, you could back up your entire hard disk every day. But the time required to do this might be burdensome, and you'd spend a fortune on backup media. If spending minimal time and money on backups were your only concern, you might back up only a few crucial files once a month. Common sense suggests there must be a happy medium.

A common strategy combines normal and differential backups as follows:

  • At some regular interval, such as once a week, perform a normal backup.
  • At regular intervals between normal backups—for example, at the end of each workday—perform a differential backup.

With this strategy, if the unthinkable happens and you need to restore one or more files, you need to look in only two places to find the most recent version of any file: the most recent normal backup and the most recent differential backup.

TIP
If the capacity of your tape drive exceeds the amount of data on all your hard disks and if you ordinarily leave your computer running all the time, you can schedule a complete normal backup to run each night while you sleep. (Just remember to insert the correct tape before you quit for the day.) Normal backups created daily provide the easiest solution when you need to restore data.

How Does Backup Know Which Files to Back Up?

Like most operating systems, Windows 2000 maintains an archive attribute for each file. Every file is either marked as needing to be archived (backed up), or it isn't marked.

Whenever a program creates or modifies a file, the operating system marks the file as needing to be archived by setting the archive attribute, which indicates that the file has changed since the last archive. When Backup sees a file with the archive attribute set, it backs up the file and, if you're performing a normal or incremental backup, clears the attribute. The next time Backup runs, the archive attribute is gone (unless you've modified the file again), and Backup knows that it doesn't need to back up the file.

You can view (and set or clear) the archive attribute for a file by viewing the file's properties dialog box.

Differential backups take longer than incremental backups (and require more tape or disk space), so some users prefer to use an incremental backup as their daily backup. If you follow this strategy, don't collect more than a half-dozen or so incremental backups between normal backups. Otherwise, you might have to search through a lot of backup sets to find particular files in the event that you need to restore them from the backup tape.

TIP
For extra security, you should rotate backup tapes. For example, if you do a normal backup once a week and differential backups on the intervening days, you might want to keep one week's worth of backups on one tape and then use a different tape the following week. If disaster strikes twice—your original storage medium and your backup tape are both damaged—you'll still be able to restore files from the previous time period's backup tape. Some of the files you restore probably won't be the most current versions, but you'll be better off than if you had to re-create everything from scratch.

TIP
If possible, store your backup tapes away from your computers. Otherwise, if you experience a fire or theft, you might lose both your originals and your backups.



Running Microsoft Windows 2000 Professional
Running Microsoft Windows 2000 Professional
ISBN: 1572318384
EAN: 2147483647
Year: 2000
Pages: 317

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