Date: Tue, 19 Apr 2016 13:27:27 -0400 From: Jon Radel <jon@radel.com> To: galtsev@kicp.uchicago.edu Cc: freebsd-questions@freebsd.org Subject: Re: Raid 1+0 Message-ID: <57166A7F.2030104@radel.com> In-Reply-To: <13260.128.135.52.6.1461084740.squirrel@cosmo.uchicago.edu> References: <571533F4.8040406@bananmonarki.se> <57153E6B.6090200@gmail.com> <20160418210257.GB86917@neutralgood.org> <64031.128.135.52.6.1461017122.squirrel@cosmo.uchicago.edu> <441t61efpv.fsf@be-well.ilk.org> <13260.128.135.52.6.1461084740.squirrel@cosmo.uchicago.edu>
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This is a cryptographically signed message in MIME format. --------------ms030207010000000203090407 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: quoted-printable On 4/19/16 12:52 PM, Valeri Galtsev wrote: > Correct, we didn't hear proof of one or another. I, however, can not th= ink > of any physical mechanism that can be involved which will lead in case = of > failure of one drive to failure of another. That is why I assume events= > are (pretty much) independent. > > Personally I think you're thinking about it all wrong. I didn't catch=20 anyone claiming that failure of one drive caused the failure of another=20 (though I've not slogged through the whole thread). Only that failure=20 of drives from the same manufacturing batch have a tendency to have=20 similar lifespans, and therefore there is some correlation as to when=20 they die. They have the same design flaws. They have the same=20 substandard components. Etc., etc. Why do you think that drives=20 come with MTBF figures, and that they're not all the same for every=20 drive? That's the summary output of somebody's best estimation of the=20 failure curve for that particular model. Personally I've never had a clear cut example with disk drives, though I = did own enough 750 mb drives from brand X some years ago to learn that=20 the involved mechanism, on average, sucked compared to other brand X=20 drives, and they were not to be trusted long term. However, I once saw=20 this very clearly in LCD monitors where I had multiples of the same=20 model. Turns out that they were caught up in the big "counterfeit"=20 capacitor scandal way back when, when due to imperfect industrial=20 espionage, a manufacturer only thought they'd stolen the formula for a=20 nice electrolyte. Turns out there was one little factor they'd missed,=20 the stabilizer that kept the capacitor from dropping dead at pretty much = the same age as every other capacitor of that model. There most=20 certainly was correlation on those monitors failing. Luckily they were=20 all still in warranty. :-) --Jon Radel jon@radel.com --------------ms030207010000000203090407 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgEFADCABgkqhkiG9w0BBwEAAKCC Cq8wggSvMIIDl6ADAgECAhEA4CPLFRKDU4mtYW56VGdrITANBgkqhkiG9w0BAQsFADBvMQsw CQYDVQQGEwJTRTEUMBIGA1UEChMLQWRkVHJ1c3QgQUIxJjAkBgNVBAsTHUFkZFRydXN0IEV4 dGVybmFsIFRUUCBOZXR3b3JrMSIwIAYDVQQDExlBZGRUcnVzdCBFeHRlcm5hbCBDQSBSb290 MB4XDTE0MTIyMjAwMDAwMFoXDTIwMDUzMDEwNDgzOFowgZsxCzAJBgNVBAYTAkdCMRswGQYD VQQIExJHcmVhdGVyIE1hbmNoZXN0ZXIxEDAOBgNVBAcTB1NhbGZvcmQxGjAYBgNVBAoTEUNP TU9ETyBDQSBMaW1pdGVkMUEwPwYDVQQDEzhDT01PRE8gU0hBLTI1NiBDbGllbnQgQXV0aGVu dGljYXRpb24gYW5kIFNlY3VyZSBFbWFpbCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCC AQoCggEBAImxDdp6UxlOcFIdvFamBia3uEngludRq/HwWhNJFaO0jBtgvHpRQqd5jKQi3xdh 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