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 oAOIb2dH143992 for ; Wed, 24 Nov 2010 12:37:02 -0600 Received: from mx2.isti.cnr.it (localhost [127.0.0.1]) by cuda.sgi.com (Spam Firewall) with ESMTP id DD7071A56BD for ; Wed, 24 Nov 2010 10:38:40 -0800 (PST) Received: from mx2.isti.cnr.it (mx2.isti.cnr.it [194.119.192.4]) by cuda.sgi.com with ESMTP id g6X2QZeW8eG0uwBm for ; Wed, 24 Nov 2010 10:38:40 -0800 (PST) Received: from SCRIPT-SPFWL-DAEMON.mx.isti.cnr.it by mx.isti.cnr.it (PMDF V6.5 #31825) id <01NUN9UYWQO0LGZ9HO@mx.isti.cnr.it> for xfs@oss.sgi.com; Wed, 24 Nov 2010 19:37:50 +0100 (MET) Received: from conversionlocal.isti.cnr.it by mx.isti.cnr.it (PMDF V6.5 #31825) id <01NUN9UYRRQ8LGZ4PF@mx.isti.cnr.it> for xfs@oss.sgi.com; Wed, 24 Nov 2010 19:37:50 +0100 (MET) Received: from [192.168.7.52] (firewall.itb.cnr.it [155.253.6.254]) by mx.isti.cnr.it (PMDF V6.5 #31826) with ESMTPSA id <01NUN9UX2X2MLLWTQ8@mx.isti.cnr.it> for xfs@oss.sgi.com; Wed, 24 Nov 2010 19:37:49 +0100 (MET) Date: Wed, 24 Nov 2010 19:39:56 +0100 From: Spelic Subject: Verify filesystem is aligned to stripes Message-id: <4CED5BFC.8000906@shiftmail.org> MIME-version: 1.0 List-Id: XFS Filesystem from SGI List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: xfs-bounces@oss.sgi.com Errors-To: xfs-bounces@oss.sgi.com To: xfs@oss.sgi.com Hi there, I thought there was a way to empirically check that the filesystem is correctly aligned to RAID stripes, but my attempts fail. I don't mean by looking at sunit and swidth from xfs_info, because that would not detect if there is some LVM offset problem. I am particularly interested for parity RAIDs in MD. I was thinking at "iostat -x 1": if writes are aligned I shouldn't see any reads from the drives in a parity RAID... unfortunately this does not work: - a dd streaming write test has almost no reads even when I mount with "noalign", with sufficiently large stripe_cache_size such as 1024. If it is smaller, always reads, even if xfs is aligned. - a kernel untar will show lots of reads at any stripe_cache_size even if I'm pretty sure I aligned the stripes correctly on my 1024k x 15 data disks and the .tar.bz2 file was in cache. I tried with both xfs stripes autodetection in 2.6.37-rc2 and by specifying su and sw values by hand, which turned out to be the same; I was without LVM so I'm pretty sure alignment was correct. Why are there still lots of reads in this case? so I'm pretty clueless. Anyone has good suggestions? Thank you PS, OT: do you confirm it's not a good idea to have agsize multiple of stripe size like the mkfs warns you against? Today I offsetted it by +1 stripe unit (chunk) so that every AG begins on a different drive but performances didn't improve noticeably. Wouldn't that cause more unfilled stripes when writing? _______________________________________________ xfs mailing list xfs@oss.sgi.com http://oss.sgi.com/mailman/listinfo/xfs