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SubjectRe: precise characterization of ext3 atomicity
Mike Fedyk wrote:

>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?
>
Yes.

>
>Then you can go on to specify that you can have larger transactions if you
>make some changes to the userspace apps.
>
>
>
>
or you are a programmer who writes code....;-) It's not that hard to
write code....;-)

--
Hans


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