From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:37734) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YlDqy-00023D-EI for qemu-devel@nongnu.org; Thu, 23 Apr 2015 05:55:29 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YlDqr-00086e-5y for qemu-devel@nongnu.org; Thu, 23 Apr 2015 05:55:28 -0400 Date: Thu, 23 Apr 2015 10:55:09 +0100 From: Stefan Hajnoczi Message-ID: <20150423095509.GF8811@stefanha-thinkpad.redhat.com> References: <1428055280-12015-1-git-send-email-wency@cn.fujitsu.com> <1428055280-12015-2-git-send-email-wency@cn.fujitsu.com> <20150420153047.GB32653@stefanha-thinkpad.redhat.com> <5535A727.5080402@cn.fujitsu.com> <55366C81.1080202@redhat.com> <20150422091803.GD6581@stefanha-thinkpad.redhat.com> <553769A1.8000509@cn.fujitsu.com> MIME-Version: 1.0 Content-Type: multipart/signed; micalg=pgp-sha1; protocol="application/pgp-signature"; boundary="K/NRh952CO+2tg14" Content-Disposition: inline In-Reply-To: <553769A1.8000509@cn.fujitsu.com> Subject: Re: [Qemu-devel] [Qemu-block] [PATCH COLO v3 01/14] docs: block replication's description List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Wen Congyang Cc: Fam Zheng , Lai Jiangshan , qemu block , Stefan Hajnoczi , Jiang Yunhong , Dong Eddie , qemu devel , Max Reitz , Gonglei , Paolo Bonzini , Yang Hongyang , "Dr. David Alan Gilbert" , zhanghailiang --K/NRh952CO+2tg14 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Content-Transfer-Encoding: quoted-printable On Wed, Apr 22, 2015 at 05:28:01PM +0800, Wen Congyang wrote: > On 04/22/2015 05:18 PM, Stefan Hajnoczi wrote: > > On Tue, Apr 21, 2015 at 05:28:01PM +0200, Paolo Bonzini wrote: > >> On 21/04/2015 03:25, Wen Congyang wrote: > >>>>> Please do not introduce "+colo" block drivers. This approach= is > >>>>> invasive and makes block replication specific to only a few block > >>>>> drivers, e.g. NBD or qcow2. > >>> NBD is used to connect to secondary qemu, so it must be used. But the= primary > >>> qemu uses quorum, so the primary disk can be any format. > >>> The secondary disk is nbd target, and it can also be any format. The = cache > >>> disk(active disk/hidden disk) is an empty disk, and it is created bef= ore run > >>> COLO. The cache disk format is qcow2 now. In theory, it can be ant fo= rmat which > >>> supports backing file. But the driver should be updated to support co= lo mode. > >>> > >>>> A cleaner approach is a QMP command or -drive options that work for = any > >>>> BlockDriverState. > >>> > >>> OK, I will add a new drive option to avoid use "+colo". > >> > >> Actually I liked the "foo+colo" names. > >> > >> These are just internal details of the implementations and the > >> primary/secondary disks actually can be any format. > >> > >> Stefan, what was your worry with the +colo block drivers? > >=20 > > Why does NBD need to know about COLO? It should be possible to use > > iSCSI or other protocols too. >=20 > Hmm, if you want to use iSCSI or other protocols, you should update the d= river > to implement block replication's control interface. >=20 > Currently, we only support nbd now. I took a quick look at the NBD patches in this series, it looks like they are a hacky way to make quorum dynamically reconfigurable. In other words, what you really need is a way to enable/disable a quorum child or even add/remove children at run-time. NBD is not the right place to implement that. Add APIs to quorum so COLO code can use them. Or maybe I'm misinterpreting the patches, I only took a quick look... Stefan --K/NRh952CO+2tg14 Content-Type: application/pgp-signature -----BEGIN PGP SIGNATURE----- Version: GnuPG v1 iQEcBAEBAgAGBQJVOMF9AAoJEJykq7OBq3PIH2QH/1CEjq+81E7gTyYxkYnmgVbd q1lIObfh/0ruZj9HlvKu0L3JwTTUismgfdTnEKdjgpPHph6qg3DpikdqgwI5KebA aoK7WVaqF3tXhUyNyy2mQ16zEYZBvwJLAqntcWywdv62mMxicMOSezUPjJCgPUd1 cYK6CjNxwn86yHECBU2roaHzD75SCCA2oIMZI1tekgMCJ5R6QN4ZrVXoYbKK+ZCC ytSBa3cw4+MdP6uv0v5CMhW0bKzicIlugX7HOItqqfWHGpCPjSYQvy++ilz1ppfO v9FYvDpG8pPuGGWIxydRIXv7k4dcLYGqLaXhhbFqqr/JDlYaHZk+kTVPkCPknDY= =VdhA -----END PGP SIGNATURE----- --K/NRh952CO+2tg14--