From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-io0-f172.google.com ([209.85.223.172]:34472 "EHLO mail-io0-f172.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751659AbbIRNM5 (ORCPT ); Fri, 18 Sep 2015 09:12:57 -0400 Received: by iofb144 with SMTP id b144so55877053iof.1 for ; Fri, 18 Sep 2015 06:12:56 -0700 (PDT) Subject: Re: FYIO: A rant about btrfs To: Duncan <1i5t5.duncan@cox.net>, linux-btrfs@vger.kernel.org References: <20150916144355.GA1285@invalid> <55F988A6.8070109@gmail.com> <55F9B357.4070505@gmail.com> <54A9EC91-FDFD-44A8-97B9-7347A89FA415@up4.com> <20150916220856.GA23830@hungrycats.org> From: Austin S Hemmelgarn Message-ID: <55FC0DCA.1080905@gmail.com> Date: Fri, 18 Sep 2015 09:12:42 -0400 MIME-Version: 1.0 In-Reply-To: Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha-512; boundary="------------ms010500010103050400010704" Sender: linux-btrfs-owner@vger.kernel.org List-ID: This is a cryptographically signed message in MIME format. --------------ms010500010103050400010704 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: quoted-printable On 2015-09-17 20:34, Duncan wrote: > Zygo Blaxell posted on Wed, 16 Sep 2015 18:08:56 -0400 as excerpted: > >> On Wed, Sep 16, 2015 at 03:04:38PM -0400, Vincent Olivier wrote: >>> >>> OK fine. Let it be clearer then (on the Btrfs wiki): nobarrier is an >>> absolute no go. Case closed. >> >> Sometimes it is useful to make an ephemeral filesystem, i.e. a btrfs o= n >> a dm-crypt device with a random key that is not stored. This >> configuration intentionally and completely destroys the entire >> filesystem, and all data on it, in the event of a power failure. It's= >> useful for things like temporary table storage, where ramfs is too >> small, swap-backed tmpfs is too slow, and/or there is a requirement th= at >> the data not be persisted across reboots. >> >> In other words, nobarrier is for a little better performance when you >> already want to _intentionally_ destroy your filesystem on power >> failure. > > Very good explanation of why it's useful to have such an otherwise > destructive mount option even available in the first place. Thanks! =3D= :^) > The other reason, as has been pointed out in a different sub-thread, is=20 that if you have a guaranteed good hardware RAID controller, which has a = known good built in non-volatile write cache, and you turn off=20 write-reordering, and you turn off the write-caches on all the connected = hard drives, then it is relatively safe. Of course, the chances of most = people actually meeting all those conditions is pretty slim. --------------ms010500010103050400010704 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 hvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMTUwOTE4MTMxMjQzWjBPBgkq hkiG9w0BCQQxQgRA1lq/g9Bx2wwEmcJO6DOB03Qs7wiJL/QuvETp2nV525TGLQYzzLXfhF1K nD+woDKkl5Apfi38Ofl7HHw3wN84pTBsBgkqhkiG9w0BCQ8xXzBdMAsGCWCGSAFlAwQBKjAL BglghkgBZQMEAQIwCgYIKoZIhvcNAwcwDgYIKoZIhvcNAwICAgCAMA0GCCqGSIb3DQMCAgFA MAcGBSsOAwIHMA0GCCqGSIb3DQMCAgEoMIGRBgkrBgEEAYI3EAQxgYMwgYAweTEQMA4GA1UE ChMHUm9vdCBDQTEeMBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlD QSBDZXJ0IFNpZ25pbmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2Vy dC5vcmcCAxBuVTCBkwYLKoZIhvcNAQkQAgsxgYOggYAweTEQMA4GA1UEChMHUm9vdCBDQTEe MBwGA1UECxMVaHR0cDovL3d3dy5jYWNlcnQub3JnMSIwIAYDVQQDExlDQSBDZXJ0IFNpZ25p bmcgQXV0aG9yaXR5MSEwHwYJKoZIhvcNAQkBFhJzdXBwb3J0QGNhY2VydC5vcmcCAxBuVTAN BgkqhkiG9w0BAQEFAASCAgAQLlHqy1XcFrzWl41x9w+QSNpeAActpvkmnPtKigPSFZ7evMqD gfE7YguuiAOViZZbCKel6y3JaP61KC0iNg4sW0tUN16trnGn6BKiYddfdj3ivSdZ7rL0KoFj xlzvaNjZlGoff5V/kjR4ScTs+MrdFU2ldPUwYqjNqYRk9H5fyqy26jzn7i8KJAxLdv6sWRik Q7h+Ve/x4LNdiAr22Pbg0bOiRUegEGBQ2Bobs22WJyAPQ7E6SSUvCWOCflQHa+q0C5QX64l+ Xcff4jPlj2vIYQ4j2oY9zgsUGnVdI95dki6tBBkxftM75opWw1n3s3xIdQ2tccNjUCBRhoyp M2kr15IEjOPbngDQfG+9wS7ol1wohgMAdeAqRCbchbCsE2RsYnKoKthkNMCATEw+0ott1UmZ TykP7rXsWtPQ5ntpZyNEZPJIN0nJi9zLNIYX/WP5Nz6eSMjhgD1CGH/yuvmS8McvIoiFO9jZ jMK8A3a99pad5QFWgORjImEW9SP3Xn9WfA67ckcOaEnNuih2zRWsMEel/92mK5V/0IfrkS8U yORlwz2PgqLicEaa71RPzTBS7TEnNl2DKDSKn79uFfqxEqAa+8scn6bb4OqbV9aKCsoAVULj M7nMGUefzzkIsVaK6WPpxFK9dGwioR0ee8EVtDInc/9/vXUOeMHVvg/cbwAAAAAAAA== --------------ms010500010103050400010704--