From owner-freebsd-fs@FreeBSD.ORG Thu Jan 28 19:54:23 2010 Return-Path: Delivered-To: freebsd-fs@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 4CE37106566B for ; Thu, 28 Jan 2010 19:54:23 +0000 (UTC) (envelope-from bfriesen@simple.dallas.tx.us) Received: from blade.simplesystems.org (blade.simplesystems.org [65.66.246.74]) by mx1.freebsd.org (Postfix) with ESMTP id 179088FC14 for ; Thu, 28 Jan 2010 19:54:22 +0000 (UTC) Received: from freddy.simplesystems.org (freddy.simplesystems.org [65.66.246.65]) by blade.simplesystems.org (8.13.8+Sun/8.13.8) with ESMTP id o0SJsEWI005710; Thu, 28 Jan 2010 13:54:14 -0600 (CST) Date: Thu, 28 Jan 2010 13:54:14 -0600 (CST) From: Bob Friesenhahn X-X-Sender: bfriesen@freddy.simplesystems.org To: Urmas Lett In-Reply-To: <4B619485.8080106@eenet.ee> Message-ID: References: <4B619485.8080106@eenet.ee> User-Agent: Alpine 2.01 (GSO 1266 2009-07-14) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.2.2 (blade.simplesystems.org [65.66.246.90]); Thu, 28 Jan 2010 13:54:14 -0600 (CST) Cc: freebsd-fs@freebsd.org Subject: Re: Reading from ZFS mirror 2x slower than expected? X-BeenThere: freebsd-fs@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Filesystems List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Thu, 28 Jan 2010 19:54:23 -0000 On Thu, 28 Jan 2010, Urmas Lett wrote: > While reading from simple zfs mirror 'dd if=zfs.test of=/dev/null bs=512k' > systat -vm shows individual disks only 50% busy: How big is the file 'zfs.test'? How was it created? If it was created from /dev/zero then its content is bogus. You need to test with non-zero data. It may be that zfs's prefetch is not working adequately. With perfect prefetch, the read rate should be doubled. Bob -- Bob Friesenhahn bfriesen@simple.dallas.tx.us, http://www.simplesystems.org/users/bfriesen/ GraphicsMagick Maintainer, http://www.GraphicsMagick.org/