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    SubjectRe: precise characterization of ext3 atomicity
    On Thu, Sep 04, 2003 at 10:37:10PM +0400, Hans Reiser wrote:
    > Mike Fedyk wrote:
    >
    > >On Thu, Sep 04, 2003 at 08:25:18PM +0400, Hans Reiser wrote:
    > >
    > >
    > >>In data=journal and data=ordered modes ext3 also guarantees that the
    > >>metadata will be committed atomically with the data they point to.
    > >>However ext3 does not provide user data atomicity guarantees beyond the
    > >>scope of a single filesystem disk block (usually 4 kilobytes). If a
    > >>single write() spans two disk blocks it is possible that a crash partway
    > >>through the write will result in only one of those blocks appearing in
    > >>the file after recovery.
    > >>
    > >>
    > >
    > >And how does reiser4 do this without changing the userspace apps?
    > >
    > We don't. We just make the hovercraft, we don't force you to go over
    > the water.....

    So by default with no user space modifications, reiser4 will be atomic for
    each write() call, and ext3 will if it aligns withing a single page.

    Is that correct?

    Then you can go on to specify that you can have larger transactions if you
    make some changes to the userspace apps.
    -
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