Date: Tue, 19 Apr 2016 17:33:22 -0400 From: Jon Radel <jon@radel.com> To: galtsev@kicp.uchicago.edu Cc: freebsd-questions@freebsd.org Subject: Re: Raid 1+0 Message-ID: <5716A422.6000707@radel.com> In-Reply-To: <44929.128.135.52.6.1461091476.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> <57166A7F.2030104@radel.com> <44929.128.135.52.6.1461091476.squirrel@cosmo.uchicago.edu>
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This is a cryptographically signed message in MIME format. --------------ms050409040707030607010608 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: quoted-printable On 4/19/16 2:44 PM, Valeri Galtsev wrote: > My opinion that your conclusion that the drives having the same MTBF=20 > (or similar lifespans) are likely to die simultaneously contradicts my = > understanding of probability theory (or statistics basics). People=20 > life expectancy in some country is 75 years. Likelyhood that two=20 > _given_ people will die at age 40 is negligible. Even twin brothers=20 > are unlikely to die during the same week or Month. This one is between = > fundamental assumptions statistics is based on. Just my humble=20 > opinion. Valeri You're confusing presence of correlation with a layman's "really, really = likely." Of course the probability that two people of the same age will die in=20 the same month is higher than the probability that two randomly selected = people will die in the same month. Likelihood of death is not constant=20 throughout life. Frankly I take the actuaries that suggest my insurance = company up my life insurance premiums every 5 years waaaaaay more=20 seriously than you. If you assume away all the interesting bits, your conclusions get pretty = useless. Actually, people study this stuff. See, for example: http://biomedgerontology.oxfordjournals.org/content/53A/6/M441.full.pdf --Jon Radel jon@radel.com --------------ms050409040707030607010608 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 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