From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:40555) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1YlE2W-0000ny-DC for qemu-devel@nongnu.org; Thu, 23 Apr 2015 06:07:28 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1YlE2R-0003VA-Tb for qemu-devel@nongnu.org; Thu, 23 Apr 2015 06:07:24 -0400 Message-ID: <5538C537.7000201@cn.fujitsu.com> Date: Thu, 23 Apr 2015 18:11:03 +0800 From: Wen Congyang MIME-Version: 1.0 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> <20150423095509.GF8811@stefanha-thinkpad.redhat.com> In-Reply-To: <20150423095509.GF8811@stefanha-thinkpad.redhat.com> Content-Type: text/plain; charset="windows-1252" Content-Transfer-Encoding: 7bit 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: Stefan Hajnoczi 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 On 04/23/2015 05:55 PM, Stefan Hajnoczi wrote: > 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 before run >>>>> COLO. The cache disk format is qcow2 now. In theory, it can be ant format which >>>>> supports backing file. But the driver should be updated to support colo 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? >>> >>> Why does NBD need to know about COLO? It should be possible to use >>> iSCSI or other protocols too. >> >> Hmm, if you want to use iSCSI or other protocols, you should update the driver >> to implement block replication's control interface. >> >> 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... Hmm, if we can enable/disable or add/remove a child at run-time, it is another choice. Thanks Wen Congyang > > Stefan >