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    SubjectRe: precise characterization of ext3 atomicity
    On Thu, Sep 04, 2003 at 11:15:40AM -0700, 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?

    It won't.


    [ snip ]
    > 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.

    There will be a new API to support userspace-controlled
    multifile transactions.

    At first stab, multifile transactions will be used internally to
    implement extended attributes.

    Now, another question is.. will the transaction API support commit() and
    rollback()? *grin*

    (wonder about coding a simple transactional database with
    shell scripts ;)

    --
    winden/network

    1. Dado un programa, siempre tiene al menos un fallo.
    2. Dadas varias lineas de codigo, siempre se pueden acortar a menos lineas.
    3. Por induccion, todos los programas se pueden
    reducir a una linea que no funciona.
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