From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f171.google.com ([209.85.213.171]:53060 "EHLO mail-ig0-f171.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752115AbaEVLKp (ORCPT ); Thu, 22 May 2014 07:10:45 -0400 Received: by mail-ig0-f171.google.com with SMTP id c1so7443015igq.4 for ; Thu, 22 May 2014 04:10:44 -0700 (PDT) Message-ID: <537DDB36.8070104@gmail.com> Date: Thu, 22 May 2014 07:10:46 -0400 From: Austin S Hemmelgarn MIME-Version: 1.0 To: Martin , linux-btrfs@vger.kernel.org Subject: Re: ditto blocks on ZFS References: <2308735.51F3c4eZQ7@xev> <4483661.BdmCOR8JR5@xev> <57f050e2a37907d810b40c5e115b28ff.squirrel@webmail.wanet.net> <1795587.Ol58oREtZ7@xev> In-Reply-To: Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha1; boundary="------------ms030407080907080607060703" Sender: linux-btrfs-owner@vger.kernel.org List-ID: This is a cryptographically signed message in MIME format. --------------ms030407080907080607060703 Content-Type: text/plain; charset=windows-1252 Content-Transfer-Encoding: quoted-printable On 2014-05-21 19:05, Martin wrote: > Very good comment from Ashford. >=20 >=20 > Sorry, but I see no advantages from Russell's replies other than for a > "feel-good" factor or a dangerous false sense of security. At best, > there is a weak justification that "for metadata, again going from 2% t= o > 4% isn't going to be a great problem" (storage is cheap and fast). >=20 > I thought an important idea behind btrfs was that we avoid by design in= > the first place the very long and vulnerable RAID rebuild scenarios > suffered for block-level RAID... >=20 >=20 > On 21/05/14 03:51, Russell Coker wrote: >> Absolutely. Hopefully this discussion will inspire the developers to >> consider this an interesting technical challenge and a feature that >> is needed to beat ZFS. >=20 > Sorry, but I think that is completely the wrong reasoning. ...Unless > that is you are some proprietary sales droid hyping features and big > numbers! :-P >=20 >=20 > Personally I'm not convinced we gain anything beyond what btrfs will > eventually offer in any case for the n-way raid or the raid-n Cauchy st= uff. >=20 > Also note that usually, data is wanted to be 100% reliable and > retrievable. Or if that fails, you go to your backups instead. Gambling= > "proportions" and "importance" rather than *ensuring* fault/error > tolerance is a very human thing... ;-) >=20 >=20 > Sorry: >=20 > Interesting idea but not convinced there's any advantage for disk/SSD > storage. >=20 >=20 > Regards, > Martin >=20 >=20 >=20 >=20 > -- > To unsubscribe from this list: send the line "unsubscribe linux-btrfs" = in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html >=20 Another nice option in this case might be adding logic to make sure that there is some (considerable) offset between copies of metadata using the dup profile (all of the filesystems that I have actually looked at the low-level on-disk structures have had both copies of the System chunks right next to each other, right at the beginning of the disk, which of course mitigates the usefulness of storing two copies of them on disk). Adding an offset in those allocations would provide some better protection against some of the more common 'idiot' failure-modes (i.e. trying to use dd to write a disk image to a USB flash drive, and accidentally overwriting the first n GB of your first HDD instead). Ideally, once we have n-way replication, System chunks should default to one copy per device for multi-device filesystems. --------------ms030407080907080607060703 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIGuDCC BrQwggScoAMCAQICAw8BRDANBgkqhkiG9w0BAQ0FADB5MRAwDgYDVQQKEwdSb290IENBMR4w HAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5vcmcxIjAgBgNVBAMTGUNBIENlcnQgU2lnbmlu ZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEWEnN1cHBvcnRAY2FjZXJ0Lm9yZzAeFw0xNDA1 MTIxNDEwMzJaFw0xNDExMDgxNDEwMzJaMGMxGDAWBgNVBAMTD0NBY2VydCBXb1QgVXNlcjEj MCEGCSqGSIb3DQEJARYUYWhmZXJyb2luN0BnbWFpbC5jb20xIjAgBgkqhkiG9w0BCQEWE2Fo ZW1tZWxnQG9oaW9ndC5jb20wggIiMA0GCSqGSIb3DQEBAQUAA4ICDwAwggIKAoICAQDbLUaL Gs4JTdU7sgr0MzD57CMUAv307ddC9pxooDMN3PiUvzEd5kLtBCh8KDB1wbMdfm4hte2rDd+j hM1tIq67BvNbdDPztOcBZwT2/3OVyyG4B1ddCqUyt03zGKw6Y34eHNfapsZiiItX0GBNfjHU Wv+WDo+XNha/WmGSSMv21HkftF9XA1KC9Bpr9JJI23MKK7T2g/7b3KoGZlx3ekLIJsF5B7+B DMPPDqOHQbRnccyOHEMyhM13g6WoAbU+3aKYc+C/9UsYtDV+xlvBLWagky1acstD5wOA35V6 uDRbUhD+vOjuMRMCj9jJOIYqa6AeSagBjxRnisJr0RFzQ4f+NjGCHPaFTvRvbkiXh4q22doT 0SxbNBUm7B9ANugIOtS9/VQhTWKDi//WTqZQ7Ecl4yVJbMCUg/iaRHMCGS41vqMICPszRidW rL04NwS9D2cREEY1y/xrNo0ZvKPZu6tLhxhPf7w+5rsN3+wWxGaR1hNpnVUT9AeacLKZO6W9 FsRT3Unkr91IhQATHTKYr4EAkjN/5lgvA+sxp5TxxsUnoJYrD8IHf8aYfJsAHMleBwx4xSeZ tw/n5iIjJjFZq9IRZ1zQhK62p+a5vJ2vlJHjTgavhQrfb1pUOjbqsnI4ndQ5hNosL9el4Kxq Yko+HsxVEmSwSsjq6cV2L3oz0z8NUwIDAQABo4IBWTCCAVUwDAYDVR0TAQH/BAIwADBWBglg hkgBhvhCAQ0ESRZHVG8gZ2V0IHlvdXIgb3duIGNlcnRpZmljYXRlIGZvciBGUkVFIGhlYWQg b3ZlciB0byBodHRwOi8vd3d3LkNBY2VydC5vcmcwDgYDVR0PAQH/BAQDAgOoMEAGA1UdJQQ5 MDcGCCsGAQUFBwMEBggrBgEFBQcDAgYKKwYBBAGCNwoDBAYKKwYBBAGCNwoDAwYJYIZIAYb4 QgQBMDIGCCsGAQUFBwEBBCYwJDAiBggrBgEFBQcwAYYWaHR0cDovL29jc3AuY2FjZXJ0Lm9y ZzAxBgNVHR8EKjAoMCagJKAihiBodHRwOi8vY3JsLmNhY2VydC5vcmcvcmV2b2tlLmNybDA0 BgNVHREELTArgRRhaGZlcnJvaW43QGdtYWlsLmNvbYETYWhlbW1lbGdAb2hpb2d0LmNvbTAN BgkqhkiG9w0BAQ0FAAOCAgEAIokFPcW8+cO2Clu0Ei+ehAmQRBHfV5RWJ8aMVLXOCfiJX0ch IjVSIt6I3uQaR4J1ZIAjCSPkbpfZQDaLoGFI5j8aYEQhOeKxrvOMzY9/aSUYabCJIhE/sX64 klFV0bzm+PR9cDMWeQ9BoZf0m8UROPSfDnrjEk+p04hGg3pAZMcSwCzxdb604NHjgHJmf2xG UQVzQgC6Ek/BKat0xuPTuPmtPv9OicK75CPmLZKYW3rFpCD6bhb1mm+ROcCNhniRY2LYm9YN QdlHQUzTFqj0tvuYrzNI3LNV4PjEfN8z6omPCT2Rq8/uKLseN+m8F0ioqm+cphqpmzKoDUpN nePLkqDFUFWCeWRxSjBTy4IMVUfdNXriVGihH8hyIICQiOfmmBOzhzUifdomJuTGtoXRuHVT R2f/YdrJrLnKI4f+Othdp7F3KhB4c6JiOnTEH5J8n9q3rFjt4MPRwcjIHMhmF5nZVQlgxEMo 1cPCmvG1D9tcgXbH79jjqydo9SDXhzLQob7axkzGRY96IstNcvoQ/UNsdPPfFMYlHtGz4TxT DhBjv4ERskGmKBZrfmxkXkcuTV/gcykct6Xvw9YXb8WTL4qSYHSYk9fReVLgE/L4RBUpX2JJ QvIR0AJLER165/aZlQXZtuJjnfxJtJTJZZ+Gor9h0G2kuR5Dy0JuYdBO4t4xggShMIIEnQIB ATCBgDB5MRAwDgYDVQQKEwdSb290IENBMR4wHAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5v cmcxIjAgBgNVBAMTGUNBIENlcnQgU2lnbmluZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEW EnN1cHBvcnRAY2FjZXJ0Lm9yZwIDDwFEMAkGBSsOAwIaBQCgggH1MBgGCSqGSIb3DQEJAzEL BgkqhkiG9w0BBwEwHAYJKoZIhvcNAQkFMQ8XDTE0MDUyMjExMTA0NlowIwYJKoZIhvcNAQkE MRYEFCD6L2L1yNrK8EBw7gyzJFtJnIi4MGwGCSqGSIb3DQEJDzFfMF0wCwYJYIZIAWUDBAEq MAsGCWCGSAFlAwQBAjAKBggqhkiG9w0DBzAOBggqhkiG9w0DAgICAIAwDQYIKoZIhvcNAwIC AUAwBwYFKw4DAgcwDQYIKoZIhvcNAwICASgwgZEGCSsGAQQBgjcQBDGBgzCBgDB5MRAwDgYD VQQKEwdSb290IENBMR4wHAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5vcmcxIjAgBgNVBAMT GUNBIENlcnQgU2lnbmluZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEWEnN1cHBvcnRAY2Fj ZXJ0Lm9yZwIDDwFEMIGTBgsqhkiG9w0BCRACCzGBg6CBgDB5MRAwDgYDVQQKEwdSb290IENB MR4wHAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5vcmcxIjAgBgNVBAMTGUNBIENlcnQgU2ln bmluZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEWEnN1cHBvcnRAY2FjZXJ0Lm9yZwIDDwFE MA0GCSqGSIb3DQEBAQUABIICAFjpfIXUfmnpU9kVtGy2B4uK+AFIkhq5wa7yRddP+uiAfh9A HqmoVHZWztiGa+sESzHuSkFRTd9FGD01A6v6FtkWClG/ThsJq6dUPz0CO/61qBap7rzvW2WY ADaQzTyMLXCTHfRqddpMGuRBID8U/GSrRJNSgs7ITMJtc9MrgxAy1d0E8yhe24OxWioMxsFP AU5CrqMOn8eJO9CqVPvCynhg9uYLazKTx9Fs3eNukZIOWt2jGDX4P95Lrmr8HYtg0WyWqqCQ VbZdRXDN2AGtTF8BGfIIAbveklEoah19qxvfN/QoGEw7yjh4lJwf19N/Nn4SjDRVLBhTh7Jy iE3+7uW81cCO7zwo6TZQoMa7zISYsOmscNShXYckZg28HAnQfoC9AjUFohuHozb/TBqaxgj/ bXS1FupB6pu6Az+duofEYla6PWSrLb/vxfGsJrowBKSyi7LBgIcssspppegKtf+Uh0kEXA+p my6Z2Sr1xfE6cvKG4xouM+dMorlq2L88QRdYGWltnEi/k3l7jeckx94x/JmZe9AtPmm53HyO Wqb0sxfrKtodmsMdPTvBcFO8md5aib1wqHza2u6VdNeHbxZILRX4vVW6QPVC7chFvPLJOkCK 6LroA+jn052U70WzlV/Jh/qEaRilo8C+FeZvlZ+iaIwn9RFjWsVK6cDeHp0rAAAAAAAA --------------ms030407080907080607060703--