From owner-freebsd-stable@FreeBSD.ORG Sun Jan 9 10:32:34 2011 Return-Path: Delivered-To: freebsd-stable@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id DCD63106564A for ; Sun, 9 Jan 2011 10:32:34 +0000 (UTC) (envelope-from hausen@punkt.de) Received: from kagate.punkt.de (kagate.punkt.de [217.29.33.131]) by mx1.freebsd.org (Postfix) with ESMTP id 671388FC08 for ; Sun, 9 Jan 2011 10:32:33 +0000 (UTC) Received: from hugo10.ka.punkt.de ([217.29.45.10]) by gate2.intern.punkt.de with ESMTP id p09ADJBp028908; Sun, 9 Jan 2011 11:13:19 +0100 (CET) Received: from [217.29.46.4] ([217.29.46.4]) by hugo10.ka.punkt.de (8.14.2/8.14.2) with ESMTP id p09ADJPs044795; Sun, 9 Jan 2011 11:13:19 +0100 (CET) (envelope-from hausen@punkt.de) Mime-Version: 1.0 (Apple Message framework v1082) Content-Type: text/plain; charset=iso-8859-1 From: "Patrick M. Hausen" In-Reply-To: <4D2987E0.7060701@infracaninophile.co.uk> Date: Sun, 9 Jan 2011 11:14:03 +0100 Content-Transfer-Encoding: quoted-printable Message-Id: <5F1A810A-E5B9-420E-89C1-4316A04B9A75@punkt.de> References: <4D1C6F90.3080206@my.gd> <4D21E679.80002@my.gd> <84882169-0461-480F-8B4C-58E794BCC8E6@my.gd> <4D297587.4030108@infracaninophile.co.uk> <4D2987E0.7060701@infracaninophile.co.uk> To: Matthew Seaman X-Mailer: Apple Mail (2.1082) Cc: freebsd-stable@freebsd.org, Jean-Yves Avenard Subject: Re: ZFS - moving from a zraid1 to zraid2 pool with 1.5tb disks X-BeenThere: freebsd-stable@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Production branch of FreeBSD source code List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 09 Jan 2011 10:32:34 -0000 Hi, all, Am 09.01.2011 um 11:03 schrieb Matthew Seaman: > [*] All of this mathematics is pretty suspect, because if two drives > fail simultaneously in a machine, the chances are the failures are not > independent, but due to some external cause [eg. like the case fan > breaking and the box toasting itself.] In which case, the comparative > chance of whatever it is affecting three or four drives at once = renders > the whole argument pointless. I assume you are familiar with these papers? http://queue.acm.org/detail.cfm?id=3D1317403 http://queue.acm.org/detail.cfm?id=3D1670144 Short version: as hard disk sizes increase to 2 TB and beyond while the = URE rate stays in the order of 1 to 10^14 blocks read, the probability of = encountering an URE during rebuild of a single parity RAID approaches 1. Best regards, Patrick --=20 punkt.de GmbH * Kaiserallee 13a * 76133 Karlsruhe Tel. 0721 9109 0 * Fax 0721 9109 100 info@punkt.de http://www.punkt.de Gf: J=FCrgen Egeling AG Mannheim 108285