[rdiff-backup-users] option to preserve every nth backup older than a certain age

[Dean Cording]

> Version: 1.2.8
> 
> Maybe rdiff-backup could get an option so that it would skip
> deleting certain backups, even if they're too old. My theory is
> that I'd like to keep daily backups for the last 60 days, but
> anything older than that should be a monthly backup.

The problem is that previous backups are not self contained - that 
is, to restore a backup from 1 April rdiffbackup needs to apply the 
diffs from ALL of the backups that were made after it.  You just 
can't delete intermediate backups without making your earlier 
backups inaccessible.

Remember, each backup only contains the differences from the 
next one, not the entire file. The only way this sort of scheme could 
be implemented is if the diffs of backups to be deleted were 
combined into the backups to be saved.  In the majority of cases 
this would not result in any saving of space and so is pretty 
pointless.

A way to achieve what you want is to run two backup archives.  
One archive is backed up daily and purges backups older than 30 
days.  The second archive is backed up once a month.   You will 
probably find though that the size of your monthly backups is 
similar to the combined size of the month's worth of daily backups.

What would be more useful is if rdiffbacjup could list every backup 
in which a specified file changed so you didn't need to go searching 
through numerous daily backups to find when it changes.


Dean