From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f172.google.com ([209.85.223.172]:34839 "EHLO mail-io0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753786AbbJUMHz (ORCPT ); Wed, 21 Oct 2015 08:07:55 -0400 Received: by iofz202 with SMTP id z202so54478753iof.2 for ; Wed, 21 Oct 2015 05:07:54 -0700 (PDT) Subject: Re: Expected behavior of bad sectors on one drive in a RAID1 To: Duncan <1i5t5.duncan@cox.net>, linux-btrfs@vger.kernel.org References: <201510201545.50705.russell@coker.com.au> <56263B0B.4050502@gmail.com> <201510210015.54337.russell@coker.com.au> <562648B5.2020401@gmail.com> <56269D1C.5080006@gmail.com> <56277C4A.70300@gmail.com> From: Austin S Hemmelgarn Message-ID: <56278012.2060206@gmail.com> Date: Wed, 21 Oct 2015 08:07:46 -0400 MIME-Version: 1.0 In-Reply-To: <56277C4A.70300@gmail.com> Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-512; boundary="------------ms060808080103060108060701" Sender: linux-btrfs-owner@vger.kernel.org List-ID: This is a cryptographically signed message in MIME format. --------------ms060808080103060108060701 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 2015-10-21 07:51, Austin S Hemmelgarn wrote: > On 2015-10-20 15:59, Austin S Hemmelgarn wrote: >> On 2015-10-20 15:20, Duncan wrote: >>> Yes, there's some small but not infinitesimal chance the checksum may= be >>> wrong, but if there's two copies of the data and the checksum on one = is >>> wrong while the checksum on the other verifies... yes, there's still >>> that >>> small chance that the one that verifies is wrong too, but that it's a= ny >>> worse than the one that does not verify? /That's/ getting close to >>> infinitesimal, or at least close enough for the purposes of a mailing= - >>> list claim without links to supporting evidence by someone who has >>> already characterized it as not mathematically rigorous... and for me= , >>> personally. I'm not spending any serious time thinking about getting= >>> hit >>> by lightening, either, tho by the same token I don't go out flying ki= tes >>> or waving long metal rods around in lightning storms, either. >> With a 32-bit checksum and a 4k block (the math is easier with smaller= >> numbers), that's 4128 bits, which means that a random single bit error= >> will have a approximately 0.24% chance of occurring in a given bit, >> which translates to an approximately 7.75% chance that it will occur i= n >> one of the checksum bits. For a 16k block it's smaller of course >> (around 1.8% I think, but that's just a guess), but it's still >> sufficiently statistically likely that it should be considered. > As mentioned in my other reply to this, I did the math wrong (bit of a > difference between kilobit and kilobyte) And I realize of course right after sending this that my other reply=20 didn't get through because GMail refuses to send mail in plain text, no=20 matter how hard I beat it over the head... --------------ms060808080103060108060701 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExDzANBglghkgBZQMEAgMFADCABgkqhkiG9w0BBwEAAKCC Brgwgga0MIIEnKADAgECAgMRLfgwDQYJKoZIhvcNAQENBQAweTEQMA4GA1UEChMHUm9vdCBD QTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNp Z25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2VydC5vcmcwHhcN MTUwOTIxMTEzNTEzWhcNMTYwMzE5MTEzNTEzWjBjMRgwFgYDVQQDEw9DQWNlcnQgV29UIFVz ZXIxIzAhBgkqhkiG9w0BCQEWFGFoZmVycm9pbjdAZ21haWwuY29tMSIwIAYJKoZIhvcNAQkB FhNhaGVtbWVsZ0BvaGlvZ3QuY29tMIICIjANBgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEA nQ/81tq0QBQi5w316VsVNfjg6kVVIMx760TuwA1MUaNQgQ3NyUl+UyFtjhpkNwwChjgAqfGd LIMTHAdObcwGfzO5uI2o1a8MHVQna8FRsU3QGouysIOGQlX8jFYXMKPEdnlt0GoQcd+BtESr pivbGWUEkPs1CwM6WOrs+09bAJP3qzKIr0VxervFrzrC5Dg9Rf18r9WXHElBuWHg4GYHNJ2V Ab8iKc10h44FnqxZK8RDN8ts/xX93i9bIBmHnFfyNRfiOUtNVeynJbf6kVtdHP+CRBkXCNRZ qyQT7gbTGD24P92PS2UTmDfplSBcWcTn65o3xWfesbf02jF6PL3BCrVnDRI4RgYxG3zFBJuG qvMoEODLhHKSXPAyQhwZINigZNdw5G1NqjXqUw+lIqdQvoPijK9J3eijiakh9u2bjWOMaleI SMRR6XsdM2O5qun1dqOrCgRkM0XSNtBQ2JjY7CycIx+qifJWsRaYWZz0aQU4ZrtAI7gVhO9h pyNaAGjvm7PdjEBiXq57e4QcgpwzvNlv8pG1c/hnt0msfDWNJtl3b6elhQ2Pz4w/QnWifZ8E BrFEmjeeJa2dqjE3giPVWrsH+lOvQQONsYJOuVb8b0zao4vrWeGmW2q2e3pdv0Axzm/60cJQ haZUv8+JdX9ZzqxOm5w5eUQSclt84u+D+hsCAwEAAaOCAVkwggFVMAwGA1UdEwEB/wQCMAAw VgYJYIZIAYb4QgENBEkWR1RvIGdldCB5b3VyIG93biBjZXJ0aWZpY2F0ZSBmb3IgRlJFRSBo ZWFkIG92ZXIgdG8gaHR0cDovL3d3dy5DQWNlcnQub3JnMA4GA1UdDwEB/wQEAwIDqDBABgNV HSUEOTA3BggrBgEFBQcDBAYIKwYBBQUHAwIGCisGAQQBgjcKAwQGCisGAQQBgjcKAwMGCWCG SAGG+EIEATAyBggrBgEFBQcBAQQmMCQwIgYIKwYBBQUHMAGGFmh0dHA6Ly9vY3NwLmNhY2Vy dC5vcmcwMQYDVR0fBCowKDAmoCSgIoYgaHR0cDovL2NybC5jYWNlcnQub3JnL3Jldm9rZS5j cmwwNAYDVR0RBC0wK4EUYWhmZXJyb2luN0BnbWFpbC5jb22BE2FoZW1tZWxnQG9oaW9ndC5j b20wDQYJKoZIhvcNAQENBQADggIBADMnxtSLiIunh/TQcjnRdf63yf2D8jMtYUm4yDoCF++J jCXbPQBGrpCEHztlNSGIkF3PH7ohKZvlqF4XePWxpY9dkr/pNyCF1PRkwxUURqvuHXbu8Lwn 8D3U2HeOEU3KmrfEo65DcbanJCMTTW7+mU9lZICPP7ZA9/zB+L0Gm1UNFZ6AU50N/86vjQfY WgkCd6dZD4rQ5y8L+d/lRbJW7ZGEQw1bSFVTRpkxxDTOwXH4/GpQfnfqTAtQuJ1CsKT12e+H NSD/RUWGTr289dA3P4nunBlz7qfvKamxPymHeBEUcuICKkL9/OZrnuYnGROFwcdvfjGE5iLB kjp/ttrY4aaVW5EsLASNgiRmA6mbgEAMlw3RwVx0sVelbiIAJg9Twzk4Ct6U9uBKiJ8S0sS2 8RCSyTmCRhJs0vvva5W9QUFGmp5kyFQEoSfBRJlbZfGX2ehI2Hi3U2/PMUm2ONuQG1E+a0AP u7I0NJc/Xil7rqR0gdbfkbWp0a+8dAvaM6J00aIcNo+HkcQkUgtfrw+C2Oyl3q8IjivGXZqT 5UdGUb2KujLjqjG91Dun3/RJ/qgQlotH7WkVBs7YJVTCxfkdN36rToPcnMYOI30FWa0Q06gn F6gUv9/mo6riv3A5bem/BdbgaJoPnWQD9D8wSyci9G4LKC+HQAMdLmGoeZfpJzKHMYIE0TCC BM0CAQEwgYAweTEQMA4GA1UEChMHUm9vdCBDQTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNl cnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNpZ25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcN AQkBFhJzdXBwb3J0QGNhY2VydC5vcmcCAxEt+DANBglghkgBZQMEAgMFAKCCAiEwGAYJKoZI hvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMTUxMDIxMTIwNzQ2WjBPBgkq hkiG9w0BCQQxQgRASiubXVpn/xBMB+daKDM4rG888wR+0KNQWgWFWI2/z25Dy/zPz8jM763h gnts8RMJLobHfAQ6PnDi6NOCEUX4ZTBsBgkqhkiG9w0BCQ8xXzBdMAsGCWCGSAFlAwQBKjAL BglghkgBZQMEAQIwCgYIKoZIhvcNAwcwDgYIKoZIhvcNAwICAgCAMA0GCCqGSIb3DQMCAgFA MAcGBSsOAwIHMA0GCCqGSIb3DQMCAgEoMIGRBgkrBgEEAYI3EAQxgYMwgYAweTEQMA4GA1UE ChMHUm9vdCBDQTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlD QSBDZXJ0IFNpZ25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2Vy dC5vcmcCAxEt+DCBkwYLKoZIhvcNAQkQAgsxgYOggYAweTEQMA4GA1UEChMHUm9vdCBDQTEe MBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNpZ25p bmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2VydC5vcmcCAxEt+DAN BgkqhkiG9w0BAQEFAASCAgAzAQ+yCcuZBvJyv+38+cbGOkeSRJrU4iEpU3Pby2nM77Sq7cyy Pq+C+BTPMbHExfwzlawqP4mfO+An0yoAJ8xOEiaiU1+erjLoc8+6k3HX+Dwq9HE6Obr8IoX1 /rQWtzAjE8OI8Pjd6jXmUewrn7GjwfwYoTykU+pnKTleqTSr6wWKibxPgcUwKCV7ShpE7E8K k0xHacTjTOGnnaHDwAFHS86yyvhpO9xRQIA9ZzCO+/L5fden9gzr6qKm5YAd5SskWS69Lm4k 2dPUGbxNrX9Xp+9AbvZHn29mD0WUbZHVk7+3hdab+RsnUt3dFRs7wjM46SqNXlSOvduDr5mr kfNJptrN8svKUuks2YdHsLJBUfBFh4HkuIvF3THaWVNhgC4Mk+/IPNNV3I9QwHi5s9XagnGq XVQA4RBJRauPhmr0vZGTQO6UpTjT0DB/osJSjZdgJNqgJJaJhL7UBGb2KpQURxJTGU80Fipd mEbVDMLyIAev3lofuLB5NvREJSqEgGr7RrQMEzcQNfDCXjAN4jYryNlB+LX6vFwyIJDoQWe2 IaVNZdJUVM1NTHwcHwc3e0Rnv5XrXUNbUxXoNUCsUJhuTX3Xthj+D6RPQv7aT0TZ3me1hbib pHgllqunh+NuiXGemej2umfLgp6EgiPfoYVxBATisNtQAKaV6mFhkX0/yQAAAAAAAA== --------------ms060808080103060108060701--