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Re: Ext3 vs. Reiser?



Hi,

On Fri, Jan 18, 2002 at 02:20:47PM +0000, Zoiah wrote:
 
> > On Fri, Jan 18, 2002 at 01:23:11PM +0000, Zoiah wrote: 
> > 
> >> I see in your benchmark that EXT3 is actually performing better than EXT2. 
> >> How is that possible? Because as far as I know EXT3 is just EXT2 + 
> >> journalling which means more work for the HD. 
> > 
> > It depends very much on the workload.  ext3 can often avoid seeks that
> > ext2 has to do, because it can flush data out sequentially to the
> > journal rather than having to seek to all the bitmap and inode blocks
> > when writing out a change to disk.  This is especially noticeable with
> > some synchronised-IO benchmarks, where ext2 has to seek all over the
> > disk for every IO request, whereas ext3 can just append a bit more to
> > the journal.
> 
> So, simply put, you can see the journal as a small on-disk cache in those 
> circumstances because the head doesn't have to search all over the disk? 

Yes, you can pretty well consider the journal to be a write-back write
cache for these purposes.  It's a write-back cache with atomic
semantics, too, which is of course how the whole recovery-on-reboot
works.

Cheers,
 Stephen





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