[Borgbackup] What to do if file is lost?

[Marian Beermann]

On 06.07.2016 17:02, Tomasz Melcer wrote:
> On 06.07.2016 15:56, Marian Beermann wrote:
>> On 06.07.2016 15:53, Tomasz Melcer wrote:
>>> My storage for backups developed a bad block (found using `btrfs
>>> scrub`). I made a copy of everything, except for one file that seem to
>>> be hit by badblock (an index.«some number») file. The original medium
>>> still seems to work fine—I mean, if not for `btrfs scrub`, I wouldn't
>>> know about the problem.
>>>
>>> […]
>>
>> index.N and hints.N are expendable. Regenerating takes a while (size of
>> repository divided by average sequential read speed).
>
> Ah, thank you. Out of curiosity, what about other files? What will
> happen if I lose one of the data files (will I just lose the chunks
> stored in that file?), or the config file?
>

The config file is "public knowledge", except if you use repokey, then
you should make backups of it (as mentioned in the docs
http://borgbackup.readthedocs.io/en/stable/quickstart.html#encrypted-repos
), since it contains the key material.

The data files is another story. There's no forward error correction in
Borg itself, so errors can be detected but only some minor errors can be
corrected. "borg check --repair" will replace corrupted data chunks with
runs of zeroes of the same length, while saying where it did that.
Corrupted commit tags can take some more data with them to nirvana.

Cheers, Marian