From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:35526) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YqelQ-00028w-Ka for qemu-devel@nongnu.org; Fri, 08 May 2015 05:40:13 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YqelP-0002Np-I9 for qemu-devel@nongnu.org; Fri, 08 May 2015 05:40:12 -0400 Date: Fri, 8 May 2015 11:39:51 +0200 From: Kevin Wolf Message-ID: <20150508093951.GA4318@noname.redhat.com> References: <5539A78D.1020206@cn.fujitsu.com> <5539F4F6.10507@redhat.com> <5539F702.7040708@cn.fujitsu.com> <20150424085841.GC2139@work-vm> <553A070E.8030909@redhat.com> <553A0F18.4010501@cn.fujitsu.com> <553A0EA3.9080400@redhat.com> <20150427093741.GA15658@stefanha-thinkpad.redhat.com> <20150505152355.GN2126@work-vm> <20150508084250.GA11717@stefanha-thinkpad.redhat.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="LQksG6bCIzRHxTLp" Content-Disposition: inline In-Reply-To: <20150508084250.GA11717@stefanha-thinkpad.redhat.com> Subject: Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's description List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Stefan Hajnoczi Cc: Yang Hongyang , Fam Zheng , qemu block , armbru@redhat.com, jcody@redhat.com, Jiang Yunhong , Dong Eddie , "Dr. David Alan Gilbert" , qemu devel , zhanghailiang , Gonglei , Paolo Bonzini , Max Reitz , Lai Jiangshan --LQksG6bCIzRHxTLp Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable Am 08.05.2015 um 10:42 hat Stefan Hajnoczi geschrieben: > On Tue, May 05, 2015 at 04:23:56PM +0100, Dr. David Alan Gilbert wrote: > > * Stefan Hajnoczi (stefanha@redhat.com) wrote: > > > On Fri, Apr 24, 2015 at 11:36:35AM +0200, Paolo Bonzini wrote: > > > >=20 > > > >=20 > > > > On 24/04/2015 11:38, Wen Congyang wrote: > > > > >> >=20 > > > > >> > That can be done with drive-mirror. But I think it's too earl= y for that. > > > > > Do you mean use drive-mirror instead of quorum? > > > >=20 > > > > Only before starting up a new secondary. Basically you do a migrat= ion > > > > with non-shared storage, and then start the secondary in colo mode. > > > >=20 > > > > But it's only for the failover case. Quorum (or a new block/colo.c > > > > driver or filter) is fine for normal colo operation. > > >=20 > > > Perhaps this patch series should mirror the Secondary's disk to a Bac= kup > > > Secondary so that the system can be protected very quickly after > > > failover. > > >=20 > > > I think anyone serious about fault tolerance would deploy a Backup > > > Secondary, otherwise the system cannot survive two failures unless a > > > human administrator is lucky/fast enough to set up a new Secondary. > >=20 > > I'd assumed that a higher level management layer would do the allocation > > of a new secondary after the first failover, so no human need be involv= ed. >=20 > That doesn't help, after the first failover is too late even if it's > done by a program. There should be no window during which the VM is > unprotected. >=20 > People who want fault tolerance care about 9s of availability. The VM > must be protected on the new Primary as soon as the failover occurs, > otherwise this isn't a serious fault tolerance solution. If you're worried about two failures in a row, why wouldn't you be worried about three in a row? I think if you really want more than one backup to be ready, you shouldn't go to two, but to n. Kevin --LQksG6bCIzRHxTLp Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v2.0.22 (GNU/Linux) iQIcBAEBAgAGBQJVTIRnAAoJEH8JsnLIjy/WecwP/3vQYH5gJKAeY3zi6P6/MXTK /54G5EwEHjbiUCE5QqoJ4cnypoWAXL3YfgrukYw71r8h0Q36AJGWrd7Fmes4s2Y0 4QmuFext1odNt+43Eo+YfapnUDg+EiVmigBLvoIw51VuGJYs2bEw/OPFK0cmgXN0 t76WadHDzkd58pMC+hVAkumkDe6p3fcAgUROT33EeHjs7kVjUO1u2Lb1Jebu3N5h rPudZzt8s8Ee/+/MTOf3lSQfljXlD7ssNkAgMvxnxHUx33siG3eP9B67urH2pZ/k l+lgEeLy6DN8SoX/HMuksDKudUJY209XN0CsI3SAWYx+D1F3DfERdE12Hht09MSz Ewy/wEHhnAqLWP/vhvfLQsQdb1NfaFaxqK2EucPz6QtPeNKbDo6cKL01QZP6z0D8 vjliKK7Ci1VKv9FzO4sMROCy3CTNEVdE+veXoQMUg0dauBup7GKXt1OicyRte4To 12QryeM1N00o9XAD/zdbdyaWAHQC2foOU+u8xlPh+LgS/aoU7KlPeiyPl0BZnnTi 3zNnbQ7/nPBfF3tIIPLWn0cpQX7bSgEceSR7820VU4M6APt7t72r//IJ7IEUxdX2 xBrkJBrrS4gfeJPraYT4bSDO2NZNVfeAYGK2DidU3tkmrsnsLWBfD66fTmXAls7V S41cAr//UFG6vCRKu4Ca =DVmS -----END PGP SIGNATURE----- --LQksG6bCIzRHxTLp--