Date: Sun, 9 Jan 2011 11:14:03 +0100 From: "Patrick M. Hausen" <hausen@punkt.de> To: Matthew Seaman <m.seaman@infracaninophile.co.uk> Cc: freebsd-stable@freebsd.org, Jean-Yves Avenard <jyavenard@gmail.com> Subject: Re: ZFS - moving from a zraid1 to zraid2 pool with 1.5tb disks Message-ID: <5F1A810A-E5B9-420E-89C1-4316A04B9A75@punkt.de> In-Reply-To: <4D2987E0.7060701@infracaninophile.co.uk> References: <4D1C6F90.3080206@my.gd> <ifsia5$5ub$2@dough.gmane.org> <4D21E679.80002@my.gd> <84882169-0461-480F-8B4C-58E794BCC8E6@my.gd> <BEBC15BA440AB24484C067A3A9D38D7E0149F32D13E3@server7.acsi.ca> <m262ty39th.wl%randy@psg.com> <4D297587.4030108@infracaninophile.co.uk> <AANLkTikn2G_23M3PbERTo8KR3sDqxkhWr=OntA4cVwh9@mail.gmail.com> <4D2987E0.7060701@infracaninophile.co.uk>
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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
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