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

[Ric Wheeler]

Bruno Wolff III wrote:
> 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.

I will send you the test code that I use & some test runs,

ric