delta backup: two full backups all the time - we don't know why :(

[vmpr]

Hi everyone

we have a strange behaviour at the moment, we have a delta backup job configured like that:

• Full backup interval is 0 as we want full backups only on Saturday night
• We have one schedule for Sunday to Friday night with no forced full backup for incremental backups
• We have one schedule for Saturday with Force Fullbackup enabled to make sure only Saturday is the full backup

Screenshot 2025-04-15 at 21.29.47.png

So, now problem is we have two full backups on our remote, and we are getting into storage space trouble

Screenshot 2025-04-15 at 15.11.58.png

Has anybody an idea why this is happening? What do I miss?

cheers and have a great day!
Ringo

[Danp]

Hi,

This is the expected behavior. The oldest backup will always be a full (key) backup, and newer incremental backups will be merged into this backup as you exceed the retention schedule. When you take the full backup on Saturdays, that doesn't eliminate the need for this prior full backup. Thus you end up with two full backups for a period of time.

[vmpr]

@Danp very interesting! Thank you! So is it somehow possible that we only do full-backups on Saturday night and only have one fullbackup? Our backup storage is almost full, and we need to make some space, so getting rid of double full backups would be great cheers Ringo

[florent]

@vmpr the oldest one is always a full
a delta is the difference between this backup and the previous, thus we need

You could do infinite delta, without making full, but this comes with a risk : if anything goes wrong ( on backup or storage) , you'll lose the full backup chain

Would it be possible to store a shorter chain here , and use a mirror backup to do longer retention on a cheaper storage ?

[vmpr]

@florent Thanks for the Tip!

The risk of an infinite delta and losing the backup chain if something goes wrong is a bit too high I bet if something goes wrong exactly in that moment, we need a reliable backup chain

Sadly, we do not have "cheaper" storage for mirror backup, as it's only a small setup for a small company.

This situation is a bit of a pickle if you want one full backup on a certain day, plus deltas, but not two full backups all the time

Is there any chance that this will change in the future to make that situation happen?

[florent]

@vmpr there is a high chance that we improve the scheduler , so maybe be able to plan more precisely when the full occurs, but we will always keep one full backup as the beginning of the chain

You can mitigate the risk on infinite schedule by using health check : restoring the backup automatically after the job, this ensure that , at the time of backup, the files are correct, and that if an issue occurs in the backup you can start a new chain, thus detecting a backup storage issue before needed it after having a production issue