From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ig0-f178.google.com ([209.85.213.178]:35157 "EHLO mail-ig0-f178.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751043AbbKLNEd (ORCPT ); Thu, 12 Nov 2015 08:04:33 -0500 Received: by igl9 with SMTP id 9so96558592igl.0 for ; Thu, 12 Nov 2015 05:04:32 -0800 (PST) Subject: Re: [PATCH 00/15] btrfs: Hot spare and Auto replace To: Qu Wenruo , Anand Jain , linux-btrfs@vger.kernel.org References: <1447066589-3835-1-git-send-email-anand.jain@oracle.com> <5643F62D.6050703@cn.fujitsu.com> From: Austin S Hemmelgarn Message-ID: <56448E58.3070000@gmail.com> Date: Thu, 12 Nov 2015 08:04:24 -0500 MIME-Version: 1.0 In-Reply-To: <5643F62D.6050703@cn.fujitsu.com> Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-512; boundary="------------ms060708050607040301000207" Sender: linux-btrfs-owner@vger.kernel.org List-ID: This is a cryptographically signed message in MIME format. --------------ms060708050607040301000207 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 2015-11-11 21:15, Qu Wenruo wrote: > Hi Anand, > > Nice work. > But I have some small questions about it. > > Anand Jain wrote on 2015/11/09 18:56 +0800: >> These set of patches provides btrfs hot spare and auto replace support= >> for you review and comments. >> >> First, here below are the simple example steps to configure the same: >> >> Add a spare device: >> btrfs spare add /dev/sde -f > > I'm sorry but I didn't quite see the benefit of a spare device. Aside from what Duncan said (and I happen to agree with him), there is=20 also the fact that hot-spares are (at least traditionally in most RAID=20 systems) usually used with RAID5 or RAID6 (or some other parity scheme). So, to summarize: 1. Hot spares are more useful for most users in global context, and in=20 that case only if they have more than one filesystem. 2. A pool of hot spares is even more useful. 3. Assuming whole disk usage (as opposed to partitioning), the hot spare = will have no load on it until it gets used, at which point it will=20 almost always be in better physical condition than the device it=20 replaced (which is important for HA systems, in such cases you replace=20 the disk that failed, and make the new disk a hot spare) 4. Hot spares are more often used (at least from what I've seen) on=20 parity based raid systems than raid1. In the rather limited case you outlined, I would probably just use raid1 = across all three devices myself (unless they were whole disks and not=20 individual partitions, in which case I'd use a hot spare), but looking=20 beyond that at my actual usage of BTRFS (multiple filesystems with=20 multiple different raid profiles, spread across various disks), hot=20 spares are definitely useful (although they would be more useful if I=20 could specify that a given hot spare be used only for a given set of=20 filesystems). --------------ms060708050607040301000207 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 hvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMTUxMTEyMTMwNDI0WjBPBgkq hkiG9w0BCQQxQgRASxc/S0jTsICUpV9QrMTnr7xCGK9AyrCMiDeWfqciQOxPVnHyF+fXbx78 M6IuibTG9W+1/+yf/KaNVYLEGBFTeTBsBgkqhkiG9w0BCQ8xXzBdMAsGCWCGSAFlAwQBKjAL BglghkgBZQMEAQIwCgYIKoZIhvcNAwcwDgYIKoZIhvcNAwICAgCAMA0GCCqGSIb3DQMCAgFA MAcGBSsOAwIHMA0GCCqGSIb3DQMCAgEoMIGRBgkrBgEEAYI3EAQxgYMwgYAweTEQMA4GA1UE ChMHUm9vdCBDQTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlD QSBDZXJ0IFNpZ25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2Vy dC5vcmcCAxEt+DCBkwYLKoZIhvcNAQkQAgsxgYOggYAweTEQMA4GA1UEChMHUm9vdCBDQTEe MBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNpZ25p bmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2VydC5vcmcCAxEt+DAN BgkqhkiG9w0BAQEFAASCAgAbRB5az0yIRGMgJPEoLHSNOdN5uT3npP2fqzhXJ1hRHFk2hV+N a/T4Qqj9lXg2lMnI67ygv/u0hg0n4dxWIl2Sy+r/r5D4i0mAw8CrCLBD/nm1hhQPPN9jg5Ld ucZ3TIlb2rFaVdbhN0h2uOOMjZfhdB0t+CdnsRKem6AgNhwIoFiXmSnQWYQuCL/gFcODXIK0 mb2j8YemUHW2N51nqty9RFB9jRT28x7BSBW5r4/SzpGpC4TWJN+w0BMndCql5IH6NUu8kIx0 YHFjJdL+EFaCYIpbYWA/SyJkXb8rmqJ8igjkJv8X9XChss/QVX5fpseufzbZRCcxOUaOJC3B /lPrBRiT4rNZcs8L7EkZCVe6CXG1Q5EREqJ04bsWug9Kkef0ihDEbDzq4K7zKTcnEC4q2LvC 2h1AlN09/JC33W2cqGUx3fwDdjqV03BSkFVyHYghxXPzWqemjJUQkw6y0lCX1oX6qtyg0kjp fQwMptEGqCA/wGhhY1Eb1BWofOlJgeHK6AK/N+4CEyICLjjg/t83CdDEu2O28ZsHMpkZqneK Q8DY8q3yVoTzAkieNTfilqDbC7agfwq23jWpffzHNkAJc3XGFks5KhS+MTZsrotgG/QIPaiB r4c4AgXrORDP1yVCT5XgsHwcLooTSRBfQlqv71EAErW2qIrNX6HFJeQBIgAAAAAAAA== --------------ms060708050607040301000207--