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    SubjectRe: [patch] ext2/3: document conditions when reliable operation is possible
    On Mon, Aug 24, 2009 at 11:19:01AM +0000, Florian Weimer wrote:
    > > +* don't damage the old data on a failed write (ATOMIC-WRITES)
    > > +
    > > + (Thrash may get written into sectors during powerfail. And
    > > + ext3 handles this surprisingly well at least in the
    > > + catastrophic case of garbage getting written into the inode
    > > + table, since the journal replay often will "repair" the
    > > + garbage that was written into the filesystem metadata blocks.
    >
    > Isn't this by design? In other words, if the metadata doesn't survive
    > non-atomic writes, wouldn't it be an ext3 bug?

    So I got confused when I quoted your note, which I had assumed was
    exactly what Pavel had written in his documentation. In fact, what he
    had written was this:

    +Don't damage the old data on a failed write (ATOMIC-WRITES)
    +~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    +
    +Either whole sector is correctly written or nothing is written during
    +powerfail.
    +
    +....

    So he had explicitly stated that he only cared about the whole sector
    being written (or not written) in the power fail case, and not any
    other. I'd suggest changing ATOMIC-WRITES to
    ATOMIC-WRITE-ON-POWERFAIL, since the one-line summary, "Don't damage
    the old data on a failed write", is also singularly misleading.

    - Ted


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