From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from cuda.sgi.com (cuda2.sgi.com [192.48.176.25]) by oss.sgi.com (8.14.3/8.14.3/SuSE Linux 0.8) with ESMTP id n9J1Snid016920 for ; Sun, 18 Oct 2009 20:28:50 -0500 Received: from mail.internode.on.net (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id CBF9115238 for ; Sun, 18 Oct 2009 18:30:21 -0700 (PDT) Received: from mail.internode.on.net (bld-mail13.adl6.internode.on.net [150.101.137.98]) by cuda.sgi.com with ESMTP id eWVjeckjdSdHcJ5H for ; Sun, 18 Oct 2009 18:30:21 -0700 (PDT) Date: Mon, 19 Oct 2009 12:30:18 +1100 From: Dave Chinner Subject: Re: XFS mount failuer on RAID5 Message-ID: <20091019013018.GQ9464@discord.disaster> References: <389deec70910152009i7656aaf2s9d929b8b68e4e740@mail.gmail.com> <200910161019.10286@zmi.at> <4AD890D1.4010208@sandeen.net> <200910172327.05122@zmi.at> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <200910172327.05122@zmi.at> 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: Michael Monnerie Cc: xfs@oss.sgi.com On Sat, Oct 17, 2009 at 11:27:04PM +0200, Michael Monnerie wrote: > On Freitag 16 Oktober 2009 Eric Sandeen wrote: > > Actually -ssize=4k is just fine even on 512 sector disks. > > Oh funny. So what's the meaning of this argument then? Or why would one > set it to 4k? What's the diff with 512b? A hardware sector is the atomic unit of IO. 4k sectors on 512b hardware sectors means that a single 4k filesystem sector write is not necessarily atomic. This can lead to problems with torn writes at power loss or sub-filesystem-sector data loss/corruption when a hardware sector goes bad. In general, these are detected no differently to the same sector loss on a 512b filesystem sector filesystem. IIRC, the main reason for 4k sectors on MD RAID5/6 is that changing the IO alignment from 4k to 512 byte IOs (i.e. sub-page sized) causes MD to flush and invalidate the stripe cache. Hence every time XFS writes a super block, AGF, AGFL or AGI, things go much slower because of this flush/invalidate. By setting the sector size to 4k, the SB/AGF/AGFL/AGI are all 4k in size and hence IO alignment never changes and hence performance remains good. Cheers, Dave. -- Dave Chinner david@fromorbit.com _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs