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    SubjectRe: Mild filesystem corruption on ext4 (no journal)
    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


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