Re: precise characterization of ext3 atomicity

[Hans Reiser <reiser@namesys.com>]

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