From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (ext-mx02.extmail.prod.ext.phx2.redhat.com [10.5.110.6]) by int-mx08.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o4M7adhX008137 for ; Sat, 22 May 2010 03:36:39 -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 o4M7aS6T022749 for ; Sat, 22 May 2010 03:36:28 -0400 Received: from localhost (localhost [127.0.0.1]) by maude.comedia.it (Postfix) with ESMTP id AB12C86F58 for ; Sat, 22 May 2010 09:36:27 +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 JJEwi111t9VB for ; Sat, 22 May 2010 09:36:22 +0200 (CEST) Date: Sat, 22 May 2010 09:36:22 +0200 From: Luca Berra Message-ID: <20100522073622.GC12294@maude.comedia.it> References: <4BF5A883.7060503@tlinx.org> <20100521051021.GA1412@maude.comedia.it> <4BF62CBF.3070702@tlinx.org> <4BF6D60E.4020306@tlinx.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <4BF6D60E.4020306@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 Fri, May 21, 2010 at 11:50:54AM -0700, Linda A. Walsh wrote: > Lyn Rees wrote: >> > 192.00K is listed as the start of each! GRR...why would that >>> be a default...I suppose it works for someone, but it's NOT a power of 2! >>> Hmph! >> >> 192 is a multiplier of 64... so it's aligned - assuming you used the whole >> disk as a PV (you didn't partition the thing first). it is chunk aligned, not stripe aligned, reads would be ok, but writes... > Isn't 64 the amount written / disk, so the strip size is 256K? > Wouldn't that make each strip have 1 64K chunk written odd, > and the next 3 written in the next 'row'.... > I suppose maybe it doesn't matter...but when you break the pv up into > vg's and lvs, somehow it seems odd to have them all skewed by 64K... it will cause multiple R-M-W cycles fro writes that cross stripe boundary, not good. > Anyway...I wanted to redo the array anyway. I didn't like the performance > I was getting, so thought I'd try RAID 50. I was only getting 150-300 on > writes/reads on the RAID60 which seemed a bit low. I get more than that > on a a 4-data-disk RAID5 (200/400). It's a bit of pain to do all this > reconfiguring now, but better now than when they are all full! It was > a mistake to do RAID60, though I don't know if the performance on a > 10data-disk RAID6 would be any better for writes...still has to do > alot of XORing even with a hardware card. the choice between raid5 and raid6 has a lot to do with data safety. also other constraints would mandate the use of spare drives in the raid5 case. personally i prefer striping smaller redundant sets for critical data. not to say that 10 is not a power of 2 and aligning lvm becomes interesting. > I had 2x6 and am going to try 4x3disks, so my hmmm....I guess now that I > think about it my strip size was really 8, not 4, since I had 2 of them. yes it was 8 > But I'll still have a strip width of 8 with 4x3 RAID5's. I don't know if it > will be much faster or not...but guess I'll see. -- Luca Berra -- bluca@comedia.it Communication Media & Services S.r.l. /"\ \ / ASCII RIBBON CAMPAIGN X AGAINST HTML MAIL / \