Re: Archive integrity/corruption question.

Hi Leland,

everything you write is correct.I would have expected the backup action 
to detect when something gets corrupt, at time of writing, but that's 
difficult to reproduce and test, so no guarantee (if you know which 
file, you could check in past backup logs). But even if it's the case, 
that doesn't help you anymore.

The only way to address this would be to create a new repository from 
time to time, to save a new baseline.

KR, Eric

On 04/02/2026 07:48, Leland C. Best wrote:
> Hi All,
> 
> First, I've used 'rdiff-backup' for a long time (20 years?).  I've had 
> to use my backups to recover everything from a few accidentally deleted 
> files to complete system restores to bare metal (although other tools 
> are also needed to do the latter).  As such, I want to thank everybody 
> who has contributed, and is contributing, to this outstanding project.
> 
> I have a question about the integrity of a backup archive under certain 
> conditions.
> 
> As I understand it, the current (i.e. most recent) backup is simply a 
> "mirror" of the source directory.  The next most recent backup can then 
> be reconstructed by applying a set of diffs (an "increment"?) to the 
> current backup.  Another (additional) set of diffs applied to that would 
> reconstruct the next most recent backup.  And so on.
> 
> Lets suppose that, somehow, the current backup (the mirror) becomes 
> corrupted.  Given how I think things work in 'rdiff-backup', it seems to 
> me that that would mean the _entire_ archive would be corrupted.  That 
> is, doing a 'rdiff-backup regress' would _not_ recover the previous 
> backup.  Is that correct?
> 
> I'm asking because my backup server has developed _very_ intermittent 
> memory errors.  I only discovered this _because_ an 'rdiff-backup 
> verify ...' on the most recent backup failed.  [I ultimately verified it 
> was a memory problem via 'memtest86+'.] The error was of the form
> 
>     ERROR:   Computed SHA1 digest of file <some file>
>     '4e45b5128111db53558b1135898386bbaac5c4b2' doesn't match recorded
>     digest of 'a671cd065bd97e16b6c5a3cf789e37447fa13fa9'. Your backup
>     repository may be corrupted!
> 
> The point being that, if I'm understanding correctly, then at this point 
> the entire archive is now basically lost.  Again, is this correct?
> 
> Thanks in advance for any info.
> 
> Cheers
> Leland
>