On Sat, 2008-12-13 at 11:40 -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. :)
My initial thoughts were that write barriers would enhance performance,
in that, you could have write cache on. So its really more of an
expectation that wc+barriers on, performs better than wc+barriers off :)
> 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.
> > Right now a "nowcache" option and having this as default appears to make
> > more sense than defaulting to barriers.
> I don't think that turning off write cache is something the filesystem
> can do; you have to take that as an administrative step on your block
> > But I think this needs more
> > testing than just those simple high meta data load tests. Anyway I am
> > happy cause I have a way to speed up XFS ;-).
> My only hand-wavy concern is whether this has any adverse physical
> effect on the drive (no cache == lots more head movement etc?) but then
> barriers are constantly flushing/invalidating that cache, so it's
> probably a wash. And really, I have no idea. :)
> To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> the body of a message to majordomo@xxxxxxxxxxxxxxx
> More majordomo info at http://vger.kernel.org/majordomo-info.html