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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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