Re: Mild filesystem corruption on ext4 (no journal)

Alan Jenkins
2009-06-05T21:31:30Z

Eric Sandeen wrote:
> Alan Jenkins wrote:
>
>> Eric Sandeen wrote:
>>
>
>
>>> Maybe you could try some things in your shutdown script, such as
>>> explicitly fsyncing the file, or bmapping it with filefrag, or dropping
>>> caches and rereading it... see what the state is just before the
>>> shutdown compared to after the reboot.
>>>
>>> -Eric
>>>
>>>
>> Dropping caches (and running sync first) had no effect on the result of
>> md5sum. Hopefully that narrows it down a bit.
>>
>
> And did the reread after dropping caches have the right data?
>

Yes.

> Did the block numbers reported by filefrag -v change post-boot?
>

Oh, I didn't understand that's what you were asking for.

The bug report Ted linked to says it's (most likely) a writeback issue.
In which case I think the block numbers won't change. I'll check
tomorrow, and follow-up if it turns up any unexpected result.

There's also speculation that it's a core kernel issue, something that
changed since 2.6.26. Perhaps that explains how remount-ro + sync +
drop_caches can leave the correct data sitting in the pagecache, without
either writing it to disk or dropping it.

Thanks
Alan