From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f175.google.com ([209.85.223.175]:36101 "EHLO mail-io0-f175.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752531AbbH0MCT (ORCPT ); Thu, 27 Aug 2015 08:02:19 -0400 Received: by iodv127 with SMTP id v127so53870129iod.3 for ; Thu, 27 Aug 2015 05:02:18 -0700 (PDT) Subject: Re: Understanding BTRFS storage To: Duncan <1i5t5.duncan@cox.net>, linux-btrfs@vger.kernel.org References: <20150826165024.05af044f@natsu> <55DDAB1C.90406@gmail.com> From: Austin S Hemmelgarn Message-ID: <55DEFC36.5000608@gmail.com> Date: Thu, 27 Aug 2015 08:01:58 -0400 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-512; boundary="------------ms000309040906080109060409" Sender: linux-btrfs-owner@vger.kernel.org List-ID: This is a cryptographically signed message in MIME format. --------------ms000309040906080109060409 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 2015-08-26 22:58, Duncan wrote: > Austin S Hemmelgarn posted on Wed, 26 Aug 2015 08:03:40 -0400 as > excerpted: > >> On 2015-08-26 07:50, Roman Mamedov wrote: >>> On Wed, 26 Aug 2015 10:56:03 +0200 George Duffield >>> wrote: >>> >>>> I'm looking to switch from a 5x3TB mdadm raid5 array to a Btrfs base= d >>>> solution that will involve duplicating a data store on a second >>>> machine for backup purposes (the machine is only powered up for >>>> backups). >>> >>> What do you want to achieve by switching? As Btrfs RAID5/6 is not saf= e >>> yet, do you also plan to migrate to RAID10, losing in storage >>> efficiency? >>> >>> Why not use Btrfs in single-device mode on top of your mdadm RAID5/6?= >>> Can even migrate without moving any data if you currently use Ext4, a= s >>> it can be converted to Btrfs in-place. > > Someone (IIRC it was Austin H) posted what I thought was an extremely > good setup, a few weeks ago. Create two (or more) mdraid0s, and put > btrfs raid1 (or raid5/6 when it's a bit more mature, I've been > recommending waiting until 4.4 and see what the on-list reports for it > look like then) on top. The btrfs raid on top lets you use btrfs' data= > integrity features, while the mdraid0s beneath help counteract the fact= > that btrfs isn't well optimized for speed yet, the way mdraid has been.= > And the btrfs raid on top means all is not lost with a device going bad= > in the mdraid0, as would normally be the case, since the other raid0(s)= , > functioning as the remaining btrfs devices, let you rebuild the missing= > btrfs device, by recreating the missing raid0. > > Normally, that sort of raid01 is discouraged in favor of raid10, with > raid1 at the lower level and raid0 on top, for more efficient rebuilds,= > but btrfs' data integrity features change that story entirely. =3D:^) > Two additional things: 1. If you use MD RAID1 instead of RAID0, it's just as fast for reads, no = slower than on top of single disks for writes, and get's you better data = safety guarantees than even raid6 (if you do 2 MD RAID 1 devices with=20 BTRFS raid1 on top, you can lose all but one disk and still have all=20 your data). 2. I would be cautious of MD/DM RAID on the most recent kernels, the=20 clustered MD code that went in recently broke a lot of things initially, = and I'm not yet convinced that they have managed to glue everything back = together yet (I'm still having occasional problems with RAID1 and RAID10 = on LVM), so do some testing on a non-production system first. --------------ms000309040906080109060409 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 Brgwgga0MIIEnKADAgECAgMQblUwDQYJKoZIhvcNAQENBQAweTEQMA4GA1UEChMHUm9vdCBD QTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNp Z25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2VydC5vcmcwHhcN MTUwMzI1MTkzNDM4WhcNMTUwOTIxMTkzNDM4WjBjMRgwFgYDVQQDEw9DQWNlcnQgV29UIFVz 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 b20wDQYJKoZIhvcNAQENBQADggIBABr5e8W+NiTER+Q/7wiA2LxWN3UdhT3eZJjqqSlP370P KL5iWqeTfxQ67Ai/mHbJcT2PgAJ+/D2Ji+aRR03UWnU/vtOwzyDLUMstqnfl0Zs+sz/CJe7x nBA5jlpjC2DKuMVfbPze7eySaen7XSGFHKE1QoVIIpQ2kVjC4nbbJQnUbAVX1Iz29WxeVGt9 XYigz3tDPf3tglN+q23E7YjQl4abTIoM7i98yV1H9gfY8lFfKZ6jREB9+n6ie2EwS3Kat2mG tl2wBx4MfRnoSQSKsLKQ5oTwhWf0JqlFwpLfl374p0Njcykej9/jnWG8Ks1V/AXTHqI4eyIP Mf5yMZkPv7n7LS9WWKdG4Nd38iv4T2EiAaWsmgu+r81qL5CJu9AyA0SBS4ttKf6k3e63w2Mv N9R45vpQ3QhAhfWyFxFhZN95APe3YECDG3+XIRJpRYPEtHuIsOyzI70ajF93gg/BidvqKsmV MM2ccktDMfqwZXea6zey7F8Geu9R7BqjXmG2HlNuXu7e/xnHOgXf5D3wPmnRLlBhXL1Ch97a w2KjaupjpAHfFjv5kGnZXN87UvvlwzIZiKXwa3vTDwK+rrKn/sHPkfDZPSiyt/ZBIK6lX83P 34H/CzGg+Kx57rHYOIHGumIvpDa5vfWp8O0sGgawb1C2Aae4sTUVIWmIjVuGI062MYIE0TCC BM0CAQEwgYAweTEQMA4GA1UEChMHUm9vdCBDQTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNl cnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNpZ25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcN AQkBFhJzdXBwb3J0QGNhY2VydC5vcmcCAxBuVTANBglghkgBZQMEAgMFAKCCAiEwGAYJKoZI hvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMTUwODI3MTIwMTU4WjBPBgkq hkiG9w0BCQQxQgRAG67wHiRpyYGobU/TkD/oLhkBxxjzokj2Ey3zvx+0DcCtvb98GCmwO4Ph lDq1bBDmd8Bz2J0H7c+htTmxY7YSlTBsBgkqhkiG9w0BCQ8xXzBdMAsGCWCGSAFlAwQBKjAL BglghkgBZQMEAQIwCgYIKoZIhvcNAwcwDgYIKoZIhvcNAwICAgCAMA0GCCqGSIb3DQMCAgFA MAcGBSsOAwIHMA0GCCqGSIb3DQMCAgEoMIGRBgkrBgEEAYI3EAQxgYMwgYAweTEQMA4GA1UE ChMHUm9vdCBDQTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlD QSBDZXJ0IFNpZ25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2Vy dC5vcmcCAxBuVTCBkwYLKoZIhvcNAQkQAgsxgYOggYAweTEQMA4GA1UEChMHUm9vdCBDQTEe MBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNpZ25p bmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2VydC5vcmcCAxBuVTAN BgkqhkiG9w0BAQEFAASCAgBnI2um7ebRg8YknNFimDbTYTIAvS7gmFew/G3weuorIDKNt2N2 otBuXE08Kd4I9V3CoWutbtH8bpORrb8BVigR59al518I/qVXlLqyIDIX2hMoyUjLs1RN60nP NR9cPFoi9NnNhCbKxTcL/kR7tfZeXDbqHqqA9+tUEoHDDJobzsJcSJKpegaZer+FoYzhI34h 8rRUPjeiANh4cwaR2offE3/sLFqic0JNoQnerDef1pGR+8XvXzYfxmA4DO7VsDYH9g8IqbWt 77OZUfcCg8NO1vvE08/BoRURlH5lRdHF28seWmzWoZho6N8Fn7bi2PNq25JhaKjm8xPl/0Eb wpcXQT6xIZdlgnehjDjzWeaapwIYJlJuj1EHMxHn6kArB6DZXqPDpjAAro4d6ZmIqFGxZAxT emtUDMMfC7Bzcw1ZX1mdqPH8gItKXVdAyVGqvUEBqyo+b8S157gEtWeyIR3z11uLKHm8d+bI Ph5UfWjfSfUEXOVN0TE47huQfHw1L4t0k0yZqtC1Ttgya0vts92kWPOfDfIFT0yfFoVxg3eL fLgtvoTMAJpvZIyPvAsQ3lrBRKxYQ2F0oOGoox7pzl7dXx2Jer9Fap6ExMG9WcO5/7etTo11 Ysa+/2bw5Ly3sl4YGM/28/mVc3iPTL/wldgcxsno6+j7RSAwFgg4qArWEAAAAAAAAA== --------------ms000309040906080109060409--