[techtalk] RE: backup newbie

Eric Richard Turner turnere at cc.wwu.edu
Wed Nov 29 09:11:32 EST 2000

On Wed, 29 Nov 2000, Magni Onsoien wrote:

> Eh, what exactly is the difference between incremental and differential
> backups?

With differential, every file that has been changed since the last
full-system backup is saved. When you restore, all you have to do is
restore from the full-system backup then from the last differential
backup. Differential backups are nice because they are simple to restore.
However, as time increases from the prior full-system backup the
differential backups take longer.

With incremental, only files that have been changed since the last
backup (either full or incremental) are saved. When you restore, you start
by restoring the full-system backup, then you have to restore each
incremental backup that has been done since the full-system backup. The
advantage to this method is that it takes less time to do your backup than
with differential.

An example to highlight the difference between the two methods:

Let's say you do a full-system backup on Sunday. Then a worker modifies
file x on Monday, and that evening you do a backup. At this point, there
is no difference between an incremental backup and a differential backup
because only file x will be backed up. Then on Tuesday a worker modifies
file y (but not file x). When you do a backup on Tuesday evening, the
differential backup will backup files x and y, while the incremental will
only backup file y because you already have a perfectly good backup of
file x from Monday's backup.

Hope this helps,
Eric R. Turner

My public OpenPGP key can be found at

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