Re: precise characterization of ext3 atomicity

[Hans Reiser]

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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