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    SubjectRe: precise characterization of ext3 atomicity
    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.....

    >
    >Most files are written with several write() calls, so even if each call is
    >atomic, your entire file will not be there.
    >
    >Also, ext3 could claim the same atomicity if it only updated meta-data on
    >write() call boundaries, instead of block boundaries.
    >
    >
    >
    >


    --
    Hans


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