Re: 12x performance drop on md/linux+sw raid1 due to barriers [xfs]

Dave Chinner
2008-12-14T23:36:25Z

On Sat, Dec 13, 2008 at 11:40:11AM -0600, Eric Sandeen wrote:
> Martin Steigerwald wrote:
>
> > At the moment it appears to me that disabling write cache may often give
> > more performance than using barriers. And this doesn't match my
> > expectation of write barriers as a feature that enhances performance.
>
> Why do you have that expectation? I've never seen barriers advertised
> as enhancing performance. :)
>
> I do wonder why barriers on, write cache off is so slow; I'd have
> thought the barriers were a no-op. Maybe I'm missing something.

Barriers still enforce ordering in this case, so it affects the
elevator algorithm....

Cheers,

Dave.
--
Dave Chinner
david@fromorbit.com