From owner-freebsd-questions@freebsd.org Tue Apr 19 21:43:22 2016 Return-Path: Delivered-To: freebsd-questions@mailman.ysv.freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:1900:2254:206a::19:1]) by mailman.ysv.freebsd.org (Postfix) with ESMTP id A6BA7B131AF for ; Tue, 19 Apr 2016 21:43:22 +0000 (UTC) (envelope-from freebsd-questions-local@be-well.ilk.org) Received: from be-well.ilk.org (be-well.ilk.org [23.30.133.173]) by mx1.freebsd.org (Postfix) with ESMTP id 842A91AD5 for ; Tue, 19 Apr 2016 21:43:22 +0000 (UTC) (envelope-from freebsd-questions-local@be-well.ilk.org) Received: by be-well.ilk.org (Postfix, from userid 1147) id B5C7F33C27; Tue, 19 Apr 2016 17:43:19 -0400 (EDT) From: Lowell Gilbert To: "Valeri Galtsev" Cc: "Steve O'Hara-Smith" , freebsd-questions@freebsd.org Subject: Re: Raid 1+0 References: <571533F4.8040406@bananmonarki.se> <57153E6B.6090200@gmail.com> <20160418210257.GB86917@neutralgood.org> <64031.128.135.52.6.1461017122.squirrel@cosmo.uchicago.edu> <20160419153824.7b679129f82a3cd0b18b9740@sohara.org> <40267.128.135.52.6.1461098148.squirrel@cosmo.uchicago.edu> Reply-To: freebsd-questions@freebsd.org Date: Tue, 19 Apr 2016 17:43:19 -0400 In-Reply-To: <40267.128.135.52.6.1461098148.squirrel@cosmo.uchicago.edu> (Valeri Galtsev's message of "Tue, 19 Apr 2016 15:35:48 -0500 (CDT)") Message-ID: <44a8kpcm14.fsf@be-well.ilk.org> User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (berkeley-unix) MIME-Version: 1.0 Content-Type: text/plain X-BeenThere: freebsd-questions@freebsd.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: User questions List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 19 Apr 2016 21:43:22 -0000 "Valeri Galtsev" writes: > On Tue, April 19, 2016 9:38 am, Steve O'Hara-Smith wrote: >> On Mon, 18 Apr 2016 17:05:22 -0500 (CDT) >> "Valeri Galtsev" wrote: >> >>> Not correct. First of all, in most of the cases, failure of each of the >>> drives are independent events >> >> If only that were so. When the drives are as near identical as >> manufacturing can make them and have had very similar histories they >> can be expected to have very similar wear and be similarly close to >> failure at all times, which makes it likely that the load imposed by >> one failing will push another over. > > Sigh. You need suggest some physics that will make one drive affect > another (aged or not aged doesn't matter for me). Then you will have me in > your team. Correlation is not causation. It's not a big stretch to imagine that two nearly identical mechanical devices, operated in nearly identical conditions, might wear out in a nearly identical way at about the same time. There is no need for one drive to affect the other. A fair number of people believe that this in fact occurs. I've looked for evidence on the subject, and I haven't found anything (beyond anecdotes) for or against the possibility.