Can delete old incremental backups, without affect new backups?

Can delete old incremental backups, without affect new backups

   KB 22295        Last updated on 2015-08-27  

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Can delete old incremental backups, without affect new backups?


Yes, you can delete those backups, and no, they will not affect subsequent new backups. Incremental backups are dependent on full backups, but not vice versa. So consider the following backups:

Incrementals: Incr-Z-3 Incr-Z-4

Full backup: full-A Incrementals: Incr-A-1 Incr-A-2 Incr-A-3 Incr-A-4

Next full backup: full-B Incrementals: Incr-B-1 Incr-B-2 Incr-B-3 Incr-B-4

Now, incremental backups build on full backups, and are useless without them. Full backups on the other hand are completely stand-alone, and will restore on their own.

So in our example, 'Incr-Z-*' are useless, as there's no full backup for them to build on. Full backup 'full-A' can be restored, and incrementals 'Incr-A-*' can be restored on top of it, using 'full-A' as their base.

Similarly with full-B and 'Incr-B-*'. full-B doesn't need full-A, nor does it need any of the 'Incr-A-*' backups.

But what if full-B gets corrupted, and cannot be used as a base? In this case, we can use full-A as the base, and run both 'Incr-A-*' and 'Incr-B-*' backups on top of that.

So incrementals, as long as they are in the right unbroken sequence, can connect like a chain. They just need one good full backup at the beginning. But they HAVE to be unbroken. If any one incremental backup is lost/corrupted/etc, all the subsequent incrementals are useless.

Therefore if we use full-A as base, and Incr-B-3 is corrupted, we can only restore till Incr-B-2. Incr-B-4 will be, again, useless.

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Verified Against: Zimbra Collaboration 8.6, 8.5, 8.0 Date Created: 08/27/2015
Article ID:,_without_affect_new_backups%3F Date Modified: 2015-08-27

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Wiki/KB reviewed by SME1 SME2 Copyeditor Last edit by Jorge de la Cruz
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