fsync, ext3, raid (md) 1, write barriers and PATA caching

[Bruno Wolff III]

On Mon, Dec 11, 2006 at 11:14:52 -0500,
  Ric Wheeler <ric at emc.com> wrote:
> 
> You can always do a sanity test on the barrier by timing how many 
> synchronous files/sec you can create (i.e., create/write/fsync/close).  
> Speeds vary depending on what kind of drive you have, journal mode, etc, 
> but you will always see much faster times with the barrier off than on 
> while writing small files (say 10K).

That's probably a good idea in any case. Down the road I will be interested
in whether barriers work through encrypted file systems and this will be a good
test to have available.

I should get at most 120 commits per second if write barriers are working;
so I think that should be easy to detect.

Is there already a tool out there that does this? It shouldn't be hard to
write something simple, but maybe someone has written something fancy
already.