Re: precise characterization of ext3 atomicity

[Hans Reiser]

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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