From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (ext-mx10.extmail.prod.ext.phx2.redhat.com [10.5.110.14]) by int-mx10.intmail.prod.int.phx2.redhat.com (8.14.4/8.14.4) with ESMTP id oBU2glbs023834 for ; Wed, 29 Dec 2010 21:42:47 -0500 Received: from mail.bmsi.com (www.bmsi.com [24.248.44.156]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id oBU2gb4r008022 for ; Wed, 29 Dec 2010 21:42:37 -0500 Received: from bmsred.bmsi.com (bmsred.bmsi.com [192.168.9.50]) by mail.bmsi.com (8.14.3/8.14.3) with ESMTP id oBU2ga9b028345 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-SHA bits=256 verify=NO) for ; Wed, 29 Dec 2010 21:42:36 -0500 Received: from bmsred (bmsred [192.168.9.50]) by bmsred.bmsi.com (8.14.3/8.14.3) with ESMTP id oBU2gZON019770 for ; Wed, 29 Dec 2010 21:42:36 -0500 Date: Wed, 29 Dec 2010 21:42:35 -0500 (EST) From: "Stuart D. Gathman" In-Reply-To: <4D1B3F6A.4070309@shiftmail.org> Message-ID: References: <4D1A9FAF.6050401@shiftmail.org> <4D1B3F6A.4070309@shiftmail.org> MIME-Version: 1.0 Subject: Re: [linux-lvm] pvmove painfully slow on parity 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" Content-Transfer-Encoding: 7bit To: LVM general discussion and development On Wed, 29 Dec 2010, Spelic wrote: > I tried multiple times for every device with consistent results, so I'm pretty > sure these are actual numbers. > What's happening? > Apart from the amazing difference of parity raid vs nonparity raid, with > parity raid it seems to vary randomly with the number of devices and the > chunksize..? This is pretty much my experience with parity raid all around. Which is why I stick with raid1 and raid10. That said, the sequential writes of pvmove should be fast for raid5 *if* the chunks are aligned so that there is no read/modify/write cycle. 1) Perhaps your test targets are not properly aligned? 2) Perhaps the raid5 implementation (hardware? linux md? experimental lvm raid5?) does a read modify write even when it doesn't have to. Your numbers sure look like read/modify/write is happening for some reason. -- Stuart D. Gathman Business Management Systems Inc. Phone: 703 591-0911 Fax: 703 591-6154 "Confutatis maledictis, flammis acribus addictis" - background song for a Microsoft sponsored "Where do you want to go from here?" commercial.