Jason B wrote:
>  close to 
> the same way as an incremental, except it's more useful, so to say?
>
> Incidentally, unrelated, but something that's been bugging me for a while: 
> subsequent full backups hardlink to older ones that have the true copy of the 
> file, correct? That means there is no meaningful way of deleting an older 
> backup, as the parent files may be lost, rendering future links useless?
>
>   
Not quite - if it were symlinks that would be true but BackupPC uses 
hard links - with a hard link the underlying inode (which describes the 
file data) persists as long as there is at least one link to it.  When 
old backups get purged  what really happens is they gut unlinked (doing 
rm -rf on a numbered backup in the directory for an individual pc has 
the same effect).   If all the numbered backups that reference a file 
get removed then only a single link (from the pool tree) will remain.   
The nightly cleanup code looks for files with one link and removes 
them.   So you can safely delete older backups knowing that only files 
that are unique to that backup will disappear (and also knowing that you 
won't get the disk space backup until after the nightly cleanup).

John

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