From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from mx1.redhat.com (ext-mx07.extmail.prod.ext.phx2.redhat.com [10.5.110.11]) by int-mx03.intmail.prod.int.phx2.redhat.com (8.13.8/8.13.8) with ESMTP id o3LGRccW021412 for ; Wed, 21 Apr 2010 12:27:38 -0400 Received: from EXHUB016-2.exch016.msoutlookonline.net (exhub016-2.exch016.msoutlookonline.net [207.5.72.164]) by mx1.redhat.com (8.13.8/8.13.8) with ESMTP id o3LGRPjQ022426 for ; Wed, 21 Apr 2010 12:27:25 -0400 Message-ID: <4BCF276A.1040907@cfl.rr.com> Date: Wed, 21 Apr 2010 12:27:22 -0400 From: Phillip Susi MIME-Version: 1.0 References: <4BCE79B5.9070600@cajuninc.com> <1271859488.23509.3@raydesk1.bettercgi.com> <20100421153600.GA28675@us.ibm.com> In-Reply-To: <20100421153600.GA28675@us.ibm.com> Content-Transfer-Encoding: 7bit Subject: Re: [linux-lvm] Migrating LVM 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" To: LVM general discussion and development On 4/21/2010 11:36 AM, malahal@us.ibm.com wrote: > Interesting! You are doing direct I/O to avoid copying from cache to user > buffer for read and vice-versa for write, but you are losing the ability > to do them parallel! You are doing the next best, that is creating two > "dd" threads -- one for reading and another for writing. Since the pipe > is really implemented in memory, why should this be faster than normal > "dd" that uses page cache? Likely that kswapd is not kicking early > enough? Oops, my eyes missed the pipe and second dd when I made my previous comments. That is pretty good for different disks then yes... not so good for same physical disk. > Enhancing "dd" to create a reader and a writer thread would really > help, I believe. I actually have some old hacked up dd code I made once to use 16 concurrent aio requests with O_DIRECT. I need to clean it up a bit but it showed great promise.