From owner-freebsd-questions@freebsd.org Wed Apr 20 09:23:49 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 17126B15B4D for ; Wed, 20 Apr 2016 09:23:49 +0000 (UTC) (envelope-from matthew@FreeBSD.org) Received: from smtp.infracaninophile.co.uk (smtp.infracaninophile.co.uk [81.2.117.100]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (Client did not present a certificate) by mx1.freebsd.org (Postfix) with ESMTPS id 960EE12CA for ; Wed, 20 Apr 2016 09:23:48 +0000 (UTC) (envelope-from matthew@FreeBSD.org) Received: from ox-dell39.ox.adestra.com (unknown [85.199.232.226]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) (Authenticated sender: m.seaman@infracaninophile.co.uk) by smtp.infracaninophile.co.uk (Postfix) with ESMTPSA id 257641152B for ; Wed, 20 Apr 2016 09:23:44 +0000 (UTC) Authentication-Results: smtp.infracaninophile.co.uk; dmarc=none header.from=FreeBSD.org Authentication-Results: smtp.infracaninophile.co.uk/257641152B; dkim=none; dkim-atps=neutral Subject: Re: Raid 1+0 To: freebsd-questions@freebsd.org 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> <44a8kpcm14.fsf@be-well.ilk.org> From: Matthew Seaman Message-ID: <5027ef1b-fd33-5e07-3a8d-fe0ce9732b29@freebsd.org> Date: Wed, 20 Apr 2016 10:23:31 +0100 User-Agent: Mozilla/5.0 (X11; FreeBSD amd64; rv:45.0) Gecko/20100101 Thunderbird/45.0 MIME-Version: 1.0 In-Reply-To: <44a8kpcm14.fsf@be-well.ilk.org> Content-Type: multipart/signed; micalg=pgp-sha512; protocol="application/pgp-signature"; boundary="8JPBdPjffXrHQaBHhtwNnxDBAv7ScOJOb" X-Virus-Scanned: clamav-milter 0.99.1 at smtp.infracaninophile.co.uk X-Virus-Status: Clean X-Spam-Status: No, score=-0.4 required=5.0 tests=BAYES_00,RDNS_NONE, SPF_SOFTFAIL autolearn=no autolearn_force=no version=3.4.1 X-Spam-Checker-Version: SpamAssassin 3.4.1 (2015-04-28) on smtp.infracaninophile.co.uk 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: Wed, 20 Apr 2016 09:23:49 -0000 This is an OpenPGP/MIME signed message (RFC 4880 and 3156) --8JPBdPjffXrHQaBHhtwNnxDBAv7ScOJOb Content-Type: multipart/mixed; boundary="AlJjkGSRPRdAPP0imDvgQgnbX8EdmxIEv" From: Matthew Seaman To: freebsd-questions@freebsd.org Message-ID: <5027ef1b-fd33-5e07-3a8d-fe0ce9732b29@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> <44a8kpcm14.fsf@be-well.ilk.org> In-Reply-To: <44a8kpcm14.fsf@be-well.ilk.org> --AlJjkGSRPRdAPP0imDvgQgnbX8EdmxIEv Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable On 04/19/16 22:43, Lowell Gilbert wrote: > Correlation is not causation. >=20 > 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. Interestingly this argument is quite a bit stronger when applied to SSD's rather than spinning disk drives. SSDs we know have a limited number of refresh cycles for any one memory cell. As members of a RAID array, they're going to see very similar patterns of activity over their lifetimes, so they're actually quite likely to wear out at a similar time= =2E > 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. Mechanical drives are a lot more affected by external differences like vibration or temperature changes, which will act to increase the variability in their lifetimes. SSDs are intrinsically /more/ reliable during their working life, but their lifetime tends to come to a much more sharply defined end. Cheers, Matthew (who has been spending far too much time going to the datacentre to replace drives recently.) --AlJjkGSRPRdAPP0imDvgQgnbX8EdmxIEv-- --8JPBdPjffXrHQaBHhtwNnxDBAv7ScOJOb Content-Type: application/pgp-signature; name="signature.asc" Content-Description: OpenPGP digital signature Content-Disposition: attachment; filename="signature.asc" -----BEGIN PGP SIGNATURE----- iQIcBAEBCgAGBQJXF0qaAAoJEABRPxDgqeTnKA4P/R1mtBargXP3BrpJyKtI3KLS pVS/26BAuLfPxVq/U/EK8wp5dEsUziCIh9lrZgwLS8OxTYaB3kfZO11kM49XMu/Y B8wQmnnVjeG18HlYaHRPcvJ1ELDe8TD334t/RzXTK4clnYqMmJl5Df6UZbOXUCIL dAbzW0nNhcsClqpZV4xBvGn1ZAGfK9aFTmofqN+4eZUqd+A9YROjBqzzpFzRCnDR BDJ9tuVctVlnt/iMiG+bvlrWkw7m2X8HEajGLjnLYz659xUp2S+WsK+KvKaXOcql oqZWTKYV1CmeAbBxYov9vxesewfMhFmfK9Mdg/318+IDxzY4V0mPdNM0qROBQJG4 O8bWfyrV+bm0y3aC4dkLj+GzC2RtRXAIH4p2Q6bzKnrU8HHlv4dSKRSzpPH1/948 /IbkHby3wnZZmwhoJYRGGVo0EJbNLDaCkjzUBKgw1zO6yxAqvyIeIfdtbsjjGDnJ 6zABr0wvQkg6s2GVR1kGYmaeJkoVJndH6Ez0mg26NRQOlwTElJgTWPMvTtaLns0q pOIAj57fLTXiOccK5codnzab3j4HLf9oYkNi8Jm2TjcpFsO5tpbFuBDJ2ZAomRez LIEJffXPwAOAdyMhJ0ljW2HHMrtl1Ib7dcxjYBFxNWvrxz+RFXYZ18p+CAj01LRU tbtT+KZIGIV70g7TN6ev =hjLE -----END PGP SIGNATURE----- --8JPBdPjffXrHQaBHhtwNnxDBAv7ScOJOb--