From mboxrd@z Thu Jan 1 00:00:00 1970 From: Steven Haigh Subject: Re: Adding caching to existing volumes? Date: Wed, 23 Jan 2013 10:26:14 +1100 Message-ID: <50FF2016.4020802@crc.id.au> References: <17989056.10.1358618905144.JavaMail.root@zimbra> <50FBA4A6.7020709@crc.id.au> <20130122231547.GF26407@google.com> Mime-Version: 1.0 Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha1; boundary="------------ms080103060308000704030909" Return-path: In-Reply-To: <20130122231547.GF26407-hpIqsD4AKlfQT0dZR+AlfA@public.gmane.org> Sender: linux-bcache-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: linux-bcache-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-Id: linux-bcache@vger.kernel.org This is a cryptographically signed message in MIME format. --------------ms080103060308000704030909 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable On 23/01/2013 10:15 AM, Kent Overstreet wrote: > On Sun, Jan 20, 2013 at 07:02:46PM +1100, Steven Haigh wrote: >> On 20/01/2013 5:08 AM, Roy Sigurd Karlsbakk wrote: >>> Hi all >>> >>> As far as I can understand from the bcache docs, a volume cached with= bcache, must be formatted and setup for bcache in the first place. I com= e from a ZFS environment, where adding SLOG or L2ARC is done dynamically,= so I have a few questions: >>> >>> - Would it be somewhat possible to add caching to an existing volume = and its data? >>> - What would happen if the cache device dies - does the whole filesys= tem become inaccessible? >> >> I've actually been wondering a bit about this - its not exactly >> clear in the docs as to what I should do to set up bcache. >> >> In my case, I have a RAID6 over 4 x 2Tb drives. It lives as >> /dev/md2. /dev/md[01] are RAID1 on a pair of 80Gb drives for boot >> and LVM. >> >> As the system is a Xen Dom0, all the DomU (guests) run from their >> own LV on the RAID6. So - it would make sense to add bcache to >> /dev/md2. >> >> I'm a bit confused from reading the docs if I can attach to the >> existing /dev/md2 or I have to create something from scratch. >> Obviously, attaching to an existing RAID device is going to be the >> preferred method. >> >> Covering this in the docs or even on the web site would probably be >> beneficial for a lot of people - especially as I feel that this is >> getting closer to be merged with the upstream kernel. > > You've got to start from scratch, unfortunately. > > The reason is that there needs to be a bcache specific superblock on th= e > backing device so bcache can keep the cache and backing device in sync = - > and especially so you can't accidentally mount and use the backing > device without the cache. That would be bad. > > I just added an explanation to the faq - thanks for pointing it out. > http://bcache.evilpiepirate.org/FAQ Great! Thanks Kent. Although this now makes me wonder how to shift the=20 2Tb+ of data to try this... That being said, I don't have a spare SSD at = this stage, so the main thing was looking at getting a patch file to=20 then add to the kernel during compile time of the RPM packages. The hard part would be redoing the entire LVM structure again for the=20 guest OS's. --=20 Steven Haigh Email: netwiz-tY1ak9Q0PTWHXe+LvDLADg@public.gmane.org Web: http://www.crc.id.au Phone: (03) 9001 6090 - 0412 935 897 Fax: (03) 8338 0299 --------------ms080103060308000704030909 Content-Type: application/pkcs7-signature; name="smime.p7s" Content-Transfer-Encoding: base64 Content-Disposition: attachment; filename="smime.p7s" Content-Description: S/MIME Cryptographic Signature MIAGCSqGSIb3DQEHAqCAMIACAQExCzAJBgUrDgMCGgUAMIAGCSqGSIb3DQEHAQAAoIIOSjCC BjQwggQcoAMCAQICAR4wDQYJKoZIhvcNAQEFBQAwfTELMAkGA1UEBhMCSUwxFjAUBgNVBAoT DVN0YXJ0Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3VyZSBEaWdpdGFsIENlcnRpZmljYXRlIFNp Z25pbmcxKTAnBgNVBAMTIFN0YXJ0Q29tIENlcnRpZmljYXRpb24gQXV0aG9yaXR5MB4XDTA3 MTAyNDIxMDE1NVoXDTE3MTAyNDIxMDE1NVowgYwxCzAJBgNVBAYTAklMMRYwFAYDVQQKEw1T dGFydENvbSBMdGQuMSswKQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0aWZpY2F0ZSBTaWdu aW5nMTgwNgYDVQQDEy9TdGFydENvbSBDbGFzcyAxIFByaW1hcnkgSW50ZXJtZWRpYXRlIENs aWVudCBDQTCCASIwDQYJKoZIhvcNAQEBBQADggEPADCCAQoCggEBAMcJg8zOLdgasSmkLhOr lr6KMoOMpohBllVHrdRvEg/q6r8jR+EK75xCGhR8ToREoqe7zM9/UnC6TS2y9UKTpT1v7RSM zR0t6ndl0TWBuUr/UXBhPk+Kmy7bI4yW4urC+y7P3/1/X7U8ocb8VpH/Clt+4iq7nirMcNh6 qJR+xjOhV+VHzQMALuGYn5KZmc1NbJQYclsGkDxDz2UbFqE2+6vIZoL+jb9x4Pa5gNf1TwSD kOkikZB1xtB4ZqtXThaABSONdfmv/Z1pua3FYxnCFmdr/+N2JLKutIxMYqQOJebr/f/h5t95 m4JgrM3Y/w7YX9d7YAL9jvN4SydHsU6n65cCAwEAAaOCAa0wggGpMA8GA1UdEwEB/wQFMAMB Af8wDgYDVR0PAQH/BAQDAgEGMB0GA1UdDgQWBBRTcu2SnODaywFcfH6WNU7y1LhRgjAfBgNV HSMEGDAWgBROC+8apEBbpRdphzDKNGhD0EGu8jBmBggrBgEFBQcBAQRaMFgwJwYIKwYBBQUH MAGGG2h0dHA6Ly9vY3NwLnN0YXJ0c3NsLmNvbS9jYTAtBggrBgEFBQcwAoYhaHR0cDovL3d3 dy5zdGFydHNzbC5jb20vc2ZzY2EuY3J0MFsGA1UdHwRUMFIwJ6AloCOGIWh0dHA6Ly93d3cu c3RhcnRzc2wuY29tL3Nmc2NhLmNybDAnoCWgI4YhaHR0cDovL2NybC5zdGFydHNzbC5jb20v c2ZzY2EuY3JsMIGABgNVHSAEeTB3MHUGCysGAQQBgbU3AQIBMGYwLgYIKwYBBQUHAgEWImh0 dHA6Ly93d3cuc3RhcnRzc2wuY29tL3BvbGljeS5wZGYwNAYIKwYBBQUHAgEWKGh0dHA6Ly93 d3cuc3RhcnRzc2wuY29tL2ludGVybWVkaWF0ZS5wZGYwDQYJKoZIhvcNAQEFBQADggIBAAqD CH14qywGXLhjjF6uHLkjd02hcdh9hrw+VUsv+q1eeQWB21jWj3kJ96AUlPCoEGZ/ynJNScWy 6QMVQjbbMXltUfO4n4bGGdKo3awPWp61tjAFgraLJgDk+DsSvUD6EowjMTNx25GQgyYJ5RPI zKKR9tQW8gGK+2+RHxkUCTbYFnL6kl8Ch507rUdPPipJ9CgJFws3kDS3gOS5WFMxcjO5DwKf KSETEPrHh7p5shuuNktvsv6hxHTLhiMKX893gxdT3XLS9OKmCv87vkINQcNEcIIoFWbP9HOR z9v3vQwR4e3ksLc2JZOAFK+ssS5XMEoznzpihEP0PLc4dCBYjbvSD7kxgDwZ+Aj8Q9PkbvE9 sIPP7ON0fz095HdThKjiVJe6vofq+n6b1NBc8XdrQvBmunwxD5nvtTW4vtN6VY7mUCmxsCie uoBJ9OlqmsVWQvifIYf40dJPZkk9YgGTzWLpXDSfLSplbY2LL9C9U0ptvjcDjefLTvqSFc7t w1sEhF0n/qpA2r0GpvkLRDmcSwVyPvmjFBGqUp/pNy8ZuPGQmHwFi2/14+xeSUDG2bwnsYJQ G2EdJCB6luQ57GEnTA/yKZSTKI8dDQa8Sd3zfXb19mOgSF0bBdXbuKhEpuP9wirslFe6fQ1t 5j5R0xi72MZ8ikMu1RQZKCyDbMwazlHiMIIIDjCCBvagAwIBAgIDA7ikMA0GCSqGSIb3DQEB BQUAMIGMMQswCQYDVQQGEwJJTDEWMBQGA1UEChMNU3RhcnRDb20gTHRkLjErMCkGA1UECxMi U2VjdXJlIERpZ2l0YWwgQ2VydGlmaWNhdGUgU2lnbmluZzE4MDYGA1UEAxMvU3RhcnRDb20g Q2xhc3MgMSBQcmltYXJ5IEludGVybWVkaWF0ZSBDbGllbnQgQ0EwHhcNMTIwMjEzMTMzODE0 WhcNMTMwMjEzMTc1NjUzWjBXMRkwFwYDVQQNExB3bjVlU1RNM2RWOUIwMEk5MRkwFwYDVQQD DBBuZXR3aXpAY3JjLmlkLmF1MR8wHQYJKoZIhvcNAQkBFhBuZXR3aXpAY3JjLmlkLmF1MIIC IjANBgkqhkiG9w0BAQEFAAOCAg8AMIICCgKCAgEAzTaLiL78pm4Hqp7Pou4C60jt2wdvDiPt Sq6hspKk6oaST7BFeDOfoed3mvzytkjNr3C1gds3zsHulAMzRjuX2M1zPkfaj5QFkmlqQcxr +tnaf8QFpn9PrUcjpbYDYPxdcGR+SeClKzmjdxicHuYDrD8YXnbk+k8dWDaCuv5sKRQHJmIR maqUIGoVML+/kUR+sqkMpnbhOsL+E84Hg4fxLzpV3Tjf9bZbKgaspvg+BeJJCYKThBxMnZJI cQ9JzDGL4rO2BEuTXI9Ofl0+AAttBEpZeqc2rePCfA9NivKTCZ0qaFKmvM5SN7TiZUqv80rD ewTp+OLXNZEd5aa5jEDPNlznkcX0WfuKCmtyIEzT7PgHl1tOWTx7nw6FVWcB8qjC6xlyaL6W 1oS7Om3b2ka+9vSiz7DrPZzUDZuS91Fr2zIIMrrRzhN8q/JdQf8lGTydpmoRUB0z+BAcH8V/ nOcMMDogqV6/dCfywi7zFQK4AsiPSpyBAZyO53J4uPgoIzSpFj54f83KRIobHCWDU1BaU2+6 CfEoAD3iMId1tcFWTXikEThL+3oHQullq9EbPR4f3ToAU7aTZYWG4KNKrmG93KAfyCUFb+bf mt3hf1BprKIUJnpOxdZHi0KwLXVwURiB4XQKZpEWL8mRbHRdxVATKrrJAHOFTl3/s37VLprP J9kCAwEAAaOCA6swggOnMAkGA1UdEwQCMAAwCwYDVR0PBAQDAgSwMB0GA1UdJQQWMBQGCCsG AQUFBwMCBggrBgEFBQcDBDAdBgNVHQ4EFgQUS9is0NdoOI3DZ/36Zlq78IrSedgwHwYDVR0j BBgwFoAUU3Ltkpzg2ssBXHx+ljVO8tS4UYIwGwYDVR0RBBQwEoEQbmV0d2l6QGNyYy5pZC5h dTCCAiEGA1UdIASCAhgwggIUMIICEAYLKwYBBAGBtTcBAgIwggH/MC4GCCsGAQUFBwIBFiJo dHRwOi8vd3d3LnN0YXJ0c3NsLmNvbS9wb2xpY3kucGRmMDQGCCsGAQUFBwIBFihodHRwOi8v d3d3LnN0YXJ0c3NsLmNvbS9pbnRlcm1lZGlhdGUucGRmMIH3BggrBgEFBQcCAjCB6jAnFiBT dGFydENvbSBDZXJ0aWZpY2F0aW9uIEF1dGhvcml0eTADAgEBGoG+VGhpcyBjZXJ0aWZpY2F0 ZSB3YXMgaXNzdWVkIGFjY29yZGluZyB0byB0aGUgQ2xhc3MgMSBWYWxpZGF0aW9uIHJlcXVp cmVtZW50cyBvZiB0aGUgU3RhcnRDb20gQ0EgcG9saWN5LCByZWxpYW5jZSBvbmx5IGZvciB0 aGUgaW50ZW5kZWQgcHVycG9zZSBpbiBjb21wbGlhbmNlIG9mIHRoZSByZWx5aW5nIHBhcnR5 IG9ibGlnYXRpb25zLjCBnAYIKwYBBQUHAgIwgY8wJxYgU3RhcnRDb20gQ2VydGlmaWNhdGlv biBBdXRob3JpdHkwAwIBAhpkTGlhYmlsaXR5IGFuZCB3YXJyYW50aWVzIGFyZSBsaW1pdGVk ISBTZWUgc2VjdGlvbiAiTGVnYWwgYW5kIExpbWl0YXRpb25zIiBvZiB0aGUgU3RhcnRDb20g Q0EgcG9saWN5LjA2BgNVHR8ELzAtMCugKaAnhiVodHRwOi8vY3JsLnN0YXJ0c3NsLmNvbS9j cnR1MS1jcmwuY3JsMIGOBggrBgEFBQcBAQSBgTB/MDkGCCsGAQUFBzABhi1odHRwOi8vb2Nz cC5zdGFydHNzbC5jb20vc3ViL2NsYXNzMS9jbGllbnQvY2EwQgYIKwYBBQUHMAKGNmh0dHA6 Ly9haWEuc3RhcnRzc2wuY29tL2NlcnRzL3N1Yi5jbGFzczEuY2xpZW50LmNhLmNydDAjBgNV HRIEHDAahhhodHRwOi8vd3d3LnN0YXJ0c3NsLmNvbS8wDQYJKoZIhvcNAQEFBQADggEBABL6 TyHlAHW0kkHb0ZLcd/pn7Ue0B5mIWBhmta4dK8qd0hXw+/lhpWaJWR/RltCSPabxSd+Lm9Iw NWm7WP73GHAGby0TC+siwDJSk7CwDBqnVM1T3XQ5TgjfVX7h9qjVixsSWzAD++dXFmpf/344 Uf3zcG/hKJSeRtOvM/88nn4eJtrn7QFnIm4AJpHEgrqwU/0pmQBLwmEYS1G5cr04Oact2v6W L3JHOlEP8lPBAO9GtZD8UZGmBoDTNG0Rf4TnVTBGdw1sLZqpXnkcVI+rDUaFk/jb7AtCB30N 8tbm2I5ALevgjv+vNMZIQD/0AgOaylGrQwbP852lgOvMo2AdpGExggTdMIIE2QIBATCBlDCB jDELMAkGA1UEBhMCSUwxFjAUBgNVBAoTDVN0YXJ0Q29tIEx0ZC4xKzApBgNVBAsTIlNlY3Vy ZSBEaWdpdGFsIENlcnRpZmljYXRlIFNpZ25pbmcxODA2BgNVBAMTL1N0YXJ0Q29tIENsYXNz IDEgUHJpbWFyeSBJbnRlcm1lZGlhdGUgQ2xpZW50IENBAgMDuKQwCQYFKw4DAhoFAKCCAh0w GAYJKoZIhvcNAQkDMQsGCSqGSIb3DQEHATAcBgkqhkiG9w0BCQUxDxcNMTMwMTIyMjMyNjE0 WjAjBgkqhkiG9w0BCQQxFgQUNt3VMbMScmJUsfY4IUu+ftJzlTkwbAYJKoZIhvcNAQkPMV8w XTALBglghkgBZQMEASowCwYJYIZIAWUDBAECMAoGCCqGSIb3DQMHMA4GCCqGSIb3DQMCAgIA gDANBggqhkiG9w0DAgIBQDAHBgUrDgMCBzANBggqhkiG9w0DAgIBKDCBpQYJKwYBBAGCNxAE MYGXMIGUMIGMMQswCQYDVQQGEwJJTDEWMBQGA1UEChMNU3RhcnRDb20gTHRkLjErMCkGA1UE CxMiU2VjdXJlIERpZ2l0YWwgQ2VydGlmaWNhdGUgU2lnbmluZzE4MDYGA1UEAxMvU3RhcnRD b20gQ2xhc3MgMSBQcmltYXJ5IEludGVybWVkaWF0ZSBDbGllbnQgQ0ECAwO4pDCBpwYLKoZI hvcNAQkQAgsxgZeggZQwgYwxCzAJBgNVBAYTAklMMRYwFAYDVQQKEw1TdGFydENvbSBMdGQu MSswKQYDVQQLEyJTZWN1cmUgRGlnaXRhbCBDZXJ0aWZpY2F0ZSBTaWduaW5nMTgwNgYDVQQD Ey9TdGFydENvbSBDbGFzcyAxIFByaW1hcnkgSW50ZXJtZWRpYXRlIENsaWVudCBDQQIDA7ik MA0GCSqGSIb3DQEBAQUABIICAKHEP9tge2ocZNyx8ImK5oSzJh+733UWBia0tS8PMJGpRqf8 yJP9WnV7hD+JmtHon21r0ZfG3Wo22nayVoCTuqrrC4hsmSGa25HjJ6wlOQ6EKj/7Ip4MwDYn sO+/p2x/rfeN2Skr7KpFT5DS9Q2eHij5Zt9XIa7PhnyhzaMVlkpsx07zrdW9aifzjEa01jMz WJL+eYolmnIpxr1AKH9i3rtSfPK/SFZpvDCQUlCjYj9L+EneaAHYhTTR69aa1bFENWPQWCvL YwlBSaFHeHmrUaaxdDQ9kPyT5grjppYUrQ1TgiahDiPoH/q7vyIHEyCgLFA4IOQr1Ha44AB4 zvlVdSE+U1ePAH0X2g6h2iMnursh68FGDjTVByJ42Xk2jErGdAk9F1IJRjbXjmLZoWxSV4WZ 5+g9U0GS0398lH15AEoi/nM1/lEdHQ/c8Loc7vFjYyi7CY+yH7o7WcpmT2LgzEi/MBIkYnCA 3iMfscces1KfYoUi/o+pBdnSSIAPN3ybDR8DheotALSJkq98I7HslOCLE8XWZl8idTVFUlOS VN9nEPVmP37som4GsJfjJbrOxZf1bciNkHS+X/IeriNjy7HtdmE72tCI6RyufyzRM8Qc4Q+9 Oabz5/osmOkcR6biQCdcTYxs6qcudbd0oEk4cC5sZzvSoGouVCbpNzBTL47VAAAAAAAA --------------ms080103060308000704030909--