From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (ext-mx03.extmail.prod.ext.phx2.redhat.com [10.5.110.7]) by int-mx04.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o4L5AcCo008649 for ; Fri, 21 May 2010 01:10:38 -0400 Received: from maude.comedia.it (maude.comedia.it [77.93.254.181]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o4L5AR7m014331 for ; Fri, 21 May 2010 01:10:28 -0400 Received: from localhost (localhost [127.0.0.1]) by maude.comedia.it (Postfix) with ESMTP id 909CA86FFE for ; Fri, 21 May 2010 07:10:26 +0200 (CEST) Received: from maude.comedia.it ([127.0.0.1]) by localhost (maude.comedia.it [127.0.0.1]) (amavisd-new, port 10025) with LMTP id 0VDp7FBGlBoN for ; Fri, 21 May 2010 07:10:21 +0200 (CEST) Date: Fri, 21 May 2010 07:10:21 +0200 From: Luca Berra Message-ID: <20100521051021.GA1412@maude.comedia.it> References: <4BF5A883.7060503@tlinx.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4BF5A883.7060503@tlinx.org> Subject: Re: [linux-lvm] Volume alignment over RAID Reply-To: LVM general discussion and development List-Id: LVM general discussion and development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , List-Id: Content-Type: text/plain; charset="us-ascii"; format="flowed" Content-Transfer-Encoding: 7bit To: linux-lvm@redhat.com On Thu, May 20, 2010 at 02:24:19PM -0700, Linda A. Walsh wrote: > I'm a bit unclear as to where some units are applied in my RAID setup, but > was wondering how LVM interacted, could be, or should be setup so that > created volumes would be aligned properly on top of a RAID disk. note that if your rig uses fairly recent software data alignment should happen automagically. > I'm using a RAID 'chunk' size of 64k as suggested by the RAID documentation > and am using 6 disks to create a RAID6, giving 4 units of data/stripe. Does I suppose by raid you mean md, so i wonder what documentation you were looking at? I think 64k might be small as a chunk size, depending on your array size you probably want a bigger size. Then, since with a six drive raid 6 stripe size is always a power of 2, answers are easy :) > this mean my logical volume needs to be aligned on a 64K boundary, or a 256k > boundary? I.e. does 64k usually specify chunk/unit, or chunk/stripe? align to stripe size > What do I need to do to make sure my logical volumes always line up on RAID > stripe boundaries? make the volume group with pe size multiple of stripe size > I've been using default logical volume parameters, which I think use an > allocation size measured in Megabytes, so does that imply I'm automatically > aligned (as 64k and 256k both divide into 1 Meg)? Or is some offset > involved? run: pvs -o pv_name,pe_start -- Luca Berra -- bluca@comedia.it Communication Media & Services S.r.l. /"\ \ / ASCII RIBBON CAMPAIGN X AGAINST HTML MAIL / \