From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda3.sgi.com [192.48.176.15]) by oss.sgi.com (8.12.11.20060308/8.12.11/SuSE Linux 0.7) with ESMTP id mBDHeEBn010196 for ; Sat, 13 Dec 2008 11:40:14 -0600 Message-ID: <4943F37B.8080405@sandeen.net> Date: Sat, 13 Dec 2008 11:40:11 -0600 From: Eric Sandeen MIME-Version: 1.0 Subject: Re: 12x performance drop on md/linux+sw raid1 due to barriers [xfs] References: <493A9BE7.3090001@sandeen.net> (sfid-20081213_171213_704814_AA9856DD) <200812131826.25280.Martin@lichtvoll.de> In-Reply-To: <200812131826.25280.Martin@lichtvoll.de> List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: Martin Steigerwald Cc: linux-xfs@oss.sgi.com, linux-raid@vger.kernel.org, Alan Piszcz xfs@oss.sgi.com 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. > 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 devices. > 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. :) -Eric _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs