[Borgbackup] "borg check" without reading every byte

[Marian Beermann]

On 17.12.2016 21:08, John Goerzen wrote:
> So I did an experiment:
> 
> rm data/21/219999
> borg check -v --archives-only
> 
> This did not flag any errors.  Now it's possible that the segment I
> deleted was not holding metadata, and therefore never visited.  However,
> I find it odd that it didn't at least notice it was missing.  It would
> be nice to check that without reading every single bit of data to
> recheck CRCs, I guess.

That's kinda expected, since the repository check and the archives check
work on different layers... one could implement a 'shallow' repository
check like you say, but it begs the question whether that's really a
useful thing to have; corruption of the data itself is more likely and
the transaction logic ensures (on typical hardware, anyway) that the
trailing end of the repository is intact (this is checked on every
access of the repository).

Cheers, Marian

> John
> 
> On 12/15/2016 01:54 PM, Marian Beermann wrote:
>> On 15.12.2016 20:35, John Goerzen wrote:
>>> Yes, I read that, but the documentation also says this:
>>>
>>> For the repository check, "For all objects stored in the segments, all
>>> metadata... and all data is read."
>>>
>>> Although now that I reread the description of the archive check, perhaps
>>> there is a case where it does not have to reread all data.  I'll see if
>>> I can validate this.
>> Archives check only works with metadata.
>>
>>> Second, the consistency and correctness of the
>>> archive metadata is verified:
>> Cheers, Marian
>>
>>> Thanks,
>>>
>>> John
>>>
>>>
>>> On 12/15/2016 01:06 PM, Marian Beermann wrote:
>>>> Hi John
>>>>
>>>> from the check help page:
>>>>
>>>>   --repository-only     only perform repository checks
>>>>   --archives-only       only perform archives checks
>>>>
>>>> Cheers, Marian
>>>>
>>>> On 15.12.2016 19:38, John Goerzen wrote:
>>>>> Hi folks,
>>>>>
>>>>> I have a question about borg check.  I'm anticipating storing a backup
>>>>> on a remote host to which I do not have the ability to install borg
>>>>> (think sshfs or webdav or so).  From the manpage description, it looks
>>>>> as if borg check will read every bit of data in the repo at least
>>>>> twice.  Is there a way for it to check the consistency of the metadata
>>>>> trees without checking the CRC of every segment or reading every bit of
>>>>> file data?
>>>>>
>>>>> (I am pondering a move from obnam, which does have this feature)
>>>>>
>>>>> Thanks,
>>>>>
>>>>> John
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>