From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ie0-f172.google.com ([209.85.223.172]:47427 "EHLO mail-ie0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750783AbbABNm6 (ORCPT ); Fri, 2 Jan 2015 08:42:58 -0500 Received: by mail-ie0-f172.google.com with SMTP id tr6so16771619ieb.3 for ; Fri, 02 Jan 2015 05:42:57 -0800 (PST) Message-ID: <54A6A05D.6000200@gmail.com> Date: Fri, 02 Jan 2015 08:42:53 -0500 From: Austin S Hemmelgarn MIME-Version: 1.0 To: ashford@whisperpc.com, Phillip Susi CC: Jose Manuel Perez Bethencourt , Chris Murphy , "sys.syphus" , Btrfs BTRFS Subject: Re: I need to P. are we almost there yet? References: <7e0d08fddb1e0060f756690f6c82c350.squirrel@webmail.wanet.net> <54A31CAE.4020606@ubuntu.com> <40b56c60ddd4801295a92c4b11d5c08e.squirrel@webmail.wanet.net> <54A3633C.3040609@ubuntu.com> <1da0cf9a75a357c960af323aa56c7530.squirrel@webmail.wanet.net> In-Reply-To: <1da0cf9a75a357c960af323aa56c7530.squirrel@webmail.wanet.net> Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha1; boundary="------------ms090909060005080709030506" Sender: linux-btrfs-owner@vger.kernel.org List-ID: This is a cryptographically signed message in MIME format. --------------ms090909060005080709030506 Content-Type: text/plain; charset=windows-1252; format=flowed Content-Transfer-Encoding: quoted-printable On 2014-12-31 12:27, ashford@whisperpc.com wrote: > Phillip > >> I had a similar question a year or two ago ( >> specifically about raid10 ) so I both experimented and read the code >> myself to find out. I was disappointed to find that it won't do >> raid10 on 3 disks since the chunk metadata describes raid10 as a >> stripe layered on top of a mirror. >> >> Jose's point was also a good one though; one chunk may decide to >> mirror disks A and B, so a failure of A and C it could recover from, >> but a different chunk could choose to mirror on disks A and C, so that= >> chunk would be lost if A and C fail. It would probably be nice if the= >> chunk allocator tried to be more deterministic about that. > > I see this as a CRITICAL design flaw. The reason for calling it CRITIC= AL > is that System Administrators have been trained for >20 years that RAID= -10 > can usually handle a dual-disk failure, but the BTRFS implementation ha= s > effectively ZERO chance of doing so. No, some rather simple math will tell you that a 4 disk BTRFS filesystem = in raid10 mode has exactly a 50% chance of surviving a dual disk=20 failure, and that as the number of disks goes up, the chance of survival = will asymptotically approach 100% (but never reach it). This is the case for _every_ RAID-10 implementation that I have ever=20 seen, including hardware raid controllers; the only real difference is=20 in the stripe length (usually 512 bytes * half the number of disks for=20 hardware raid, 4k * half the number of disks for software raid, and the=20 filesystem block size (default is 16k in current versions) * half the=20 number of disks for BTRFS). --------------ms090909060005080709030506 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIFuDCC BbQwggOcoAMCAQICAw9gVDANBgkqhkiG9w0BAQ0FADB5MRAwDgYDVQQKEwdSb290IENBMR4w HAYDVQQLExVodHRwOi8vd3d3LmNhY2VydC5vcmcxIjAgBgNVBAMTGUNBIENlcnQgU2lnbmlu ZyBBdXRob3JpdHkxITAfBgkqhkiG9w0BCQEWEnN1cHBvcnRAY2FjZXJ0Lm9yZzAeFw0xNDA4 MDgxMTMwNDRaFw0xNTAyMDQxMTMwNDRaMGMxGDAWBgNVBAMTD0NBY2VydCBXb1QgVXNlcjEj MCEGCSqGSIb3DQEJARYUYWhmZXJyb2luN0BnbWFpbC5jb20xIjAgBgkqhkiG9w0BCQEWE2Fo ZW1tZWxnQG9oaW9ndC5jb20wggEiMA0GCSqGSIb3DQEBAQUAA4IBDwAwggEKAoIBAQDdmm8R BM5D6fGiB6rpogPZbLYu6CkU6834rcJepfmxKnLarYUYM593/VGygfaaHAyuc8qLaRA3u1M0 Qp29flqmhv1VDTBZ+zFu6JgHjTDniBii1KOZRo0qV3jC5NvaS8KUM67+eQBjm29LhBWVi3+e a8jLxmogFXV0NGej+GHIr5zA9qKz2WJOEoGh0EfqZ2MQTmozcGI43/oqIYhRj8fRMkWXLUAF WsLzPQMpK19hD8fqwlxQWhBV8gsGRG54K5pyaQsjne7m89SF5M8JkNJPH39tHEvfv2Vhf7EM Y4WGyhLAULSlym1AI1uUHR1FfJaj3AChaEJZli/AdajYsqc7AgMBAAGjggFZMIIBVTAMBgNV HRMBAf8EAjAAMFYGCWCGSAGG+EIBDQRJFkdUbyBnZXQgeW91ciBvd24gY2VydGlmaWNhdGUg Zm9yIEZSRUUgaGVhZCBvdmVyIHRvIGh0dHA6Ly93d3cuQ0FjZXJ0Lm9yZzAOBgNVHQ8BAf8E BAMCA6gwQAYDVR0lBDkwNwYIKwYBBQUHAwQGCCsGAQUFBwMCBgorBgEEAYI3CgMEBgorBgEE AYI3CgMDBglghkgBhvhCBAEwMgYIKwYBBQUHAQEEJjAkMCIGCCsGAQUFBzABhhZodHRwOi8v b2NzcC5jYWNlcnQub3JnMDEGA1UdHwQqMCgwJqAkoCKGIGh0dHA6Ly9jcmwuY2FjZXJ0Lm9y Zy9yZXZva2UuY3JsMDQGA1UdEQQtMCuBFGFoZmVycm9pbjdAZ21haWwuY29tgRNhaGVtbWVs Z0BvaGlvZ3QuY29tMA0GCSqGSIb3DQEBDQUAA4ICAQCr4klxcZU/PDRBpUtlb+d6JXl2dfto OUP/6g19dpx6Ekt2pV1eujpIj5whh5KlCSPUgtHZI7BcksLSczQbxNDvRu6LNKqGJGvcp99k cWL1Z6BsgtvxWKkOmy1vB+2aPfDiQQiMCCLAqXwHiNDZhSkwmGsJ7KHMWgF/dRVDnsl6aOQZ jAcBMpUZxzA/bv4nY2PylVdqJWp9N7x86TF9sda1zRZiyUwy83eFTDNzefYPtc4MLppcaD4g Wt8U6T2ffQfCWVzDirhg4WmDH3MybDItjkSB2/+pgGOS4lgtEBMHzAGQqQ+5PojTHRyqu9Jc O59oIGrTaOtKV9nDeDtzNaQZgygJItJi9GoAl68AmIHxpS1rZUNV6X8ydFrEweFdRTVWhUEL 70Cnx84YBojXv01LYBSZaq18K8cERPLaIrUD2go+2ffjdE9ejvYDhNBllY+ufvRizIjQA1uC OdktVAN6auQob94kOOsWpoMSrzHHvOvVW/kbokmKzaLtcs9+nJoL+vPi2AyzbaoQASVZYOGW pE3daA0F5FJfcPZKCwd5wdnmT3dU1IRUxa5vMmgjP20lkfP8tCPtvZv2mmI2Nw5SaXNY4gVu WQrvkV2in+TnGqgEIwUrLVbx9G6PSYZZs07czhO+Q1iVuKdAwjL/AYK0Us9v50acIzbl5CWw ZGj3wjGCA6EwggOdAgEBMIGAMHkxEDAOBgNVBAoTB1Jvb3QgQ0ExHjAcBgNVBAsTFWh0dHA6 Ly93d3cuY2FjZXJ0Lm9yZzEiMCAGA1UEAxMZQ0EgQ2VydCBTaWduaW5nIEF1dGhvcml0eTEh MB8GCSqGSIb3DQEJARYSc3VwcG9ydEBjYWNlcnQub3JnAgMPYFQwCQYFKw4DAhoFAKCCAfUw GAYJKoZIhvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMTUwMTAyMTM0MjUz WjAjBgkqhkiG9w0BCQQxFgQUwY+kR5DNss0pQrr+4fP3r8czymEwbAYJKoZIhvcNAQkPMV8w XTALBglghkgBZQMEASowCwYJYIZIAWUDBAECMAoGCCqGSIb3DQMHMA4GCCqGSIb3DQMCAgIA gDANBggqhkiG9w0DAgIBQDAHBgUrDgMCBzANBggqhkiG9w0DAgIBKDCBkQYJKwYBBAGCNxAE MYGDMIGAMHkxEDAOBgNVBAoTB1Jvb3QgQ0ExHjAcBgNVBAsTFWh0dHA6Ly93d3cuY2FjZXJ0 Lm9yZzEiMCAGA1UEAxMZQ0EgQ2VydCBTaWduaW5nIEF1dGhvcml0eTEhMB8GCSqGSIb3DQEJ ARYSc3VwcG9ydEBjYWNlcnQub3JnAgMPYFQwgZMGCyqGSIb3DQEJEAILMYGDoIGAMHkxEDAO BgNVBAoTB1Jvb3QgQ0ExHjAcBgNVBAsTFWh0dHA6Ly93d3cuY2FjZXJ0Lm9yZzEiMCAGA1UE AxMZQ0EgQ2VydCBTaWduaW5nIEF1dGhvcml0eTEhMB8GCSqGSIb3DQEJARYSc3VwcG9ydEBj YWNlcnQub3JnAgMPYFQwDQYJKoZIhvcNAQEBBQAEggEAGBYEwV7FCG6JQjBWWbZLBJ6MuAdZ bVXKyjmLiYkIqpnL42FGjrPCotMfm0DNwwon8TaR6enR/y5qxvId2h0ZUMtL4VU9J/Wfu7nr xrRjKNpBaydnj+xHU+RumGS7rg5tzpoOlt6mkHyiuD5f1rYb8nmpvKUPzGxbCtAe2+bv2HNl vOTRCNdHPkUUk55PnLRlyxf+ns9h8tV5KMkjLllIOTf20EtbDrf4TxCNyjj3oGvoZExs8WST gWI84yRcHPjIy/h6xz2evQOeJsqj4Ys+UJEJ8R0vtqilr9xPZwIDHI3QFITU9YqcVRUGfC7o DXSai3OaHv9YSiojuYOsYm1BiwAAAAAAAA== --------------ms090909060005080709030506--