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Subject: Re: corrupt leaf; unaligned key offset for csum item
To: Chris Murphy <lists@colorremedies.com>
Cc: Simon Kaiser <simon.kaiser@kit.edu>,
        Btrfs BTRFS <linux-btrfs@vger.kernel.org>
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From: Qu Wenruo <quwenruo.btrfs@gmx.com>
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From: Qu Wenruo <quwenruo.btrfs@gmx.com>
To: Chris Murphy <lists@colorremedies.com>
Cc: Simon Kaiser <simon.kaiser@kit.edu>,
 Btrfs BTRFS <linux-btrfs@vger.kernel.org>
Message-ID: <aa02c8c9-7ce7-eb8d-18e8-d810532083d8@gmx.com>
Subject: Re: corrupt leaf; unaligned key offset for csum item
References: <87lgboxi83.fsf@int-nb-181.i-did-not-set--mail-host-address--so-tickle-me>
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On 2018=E5=B9=B406=E6=9C=8810=E6=97=A5 11:53, Chris Murphy wrote:
> On Sat, Jun 9, 2018 at 7:56 PM, Qu Wenruo <quwenruo.btrfs@gmx.com> wrot=
e:
>>
>> Indeed, the corrupted bytenr is 0x4bc98004.
>> Looks pretty like a bit flip in the 3rd lowest bit.
>>
>> It can be fixed by manually patching the corrupted leaf to get rid of
>> the bitflip.
>> I could provide a special branch of btrfs-progs to fix it easily.
>>
>> But before that, it's better to do a scrub to see if there is other
>> similar problems, so I could fix them all.
>>
>=20
> Do you think Simon should try -o ro and -o ro,norecovery and see if he
> can update backups the easy way first?

If the bit flip is the only problem, I could fix it manually and nothing
is lost, the fs can be used as usual.

> And then use the offline scrub
> to check for additional problems?

I mean online scrub.

I didn't notice extra error, and I don't believe even for a faulty
memory, bit flip is that easy to happen, so on-line scrub should do the
work.

>=20
> Simon, the offline scrub is done unmounted with 'btrfs check
> --check-data-csum <dev>' and it is a read-only check.
>=20
>=20


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