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Date: Fri, 24 Apr 2015 09:58:42 +0100
From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>
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Subject: Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's
	description
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To: Wen Congyang <wency@cn.fujitsu.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, qemu block <qemu-block@nongnu.org>, armbru@redhat.com, jcody@redhat.com, Jiang Yunhong <yunhong.jiang@intel.com>, Dong Eddie <eddie.dong@intel.com>, qemu devel <qemu-devel@nongnu.org>, Max Reitz <mreitz@redhat.com>, Gonglei <arei.gonglei@huawei.com>, Stefan Hajnoczi <stefanha@redhat.com>, Paolo Bonzini <pbonzini@redhat.com>, Yang Hongyang <yanghy@cn.fujitsu.com>, zhanghailiang <zhang.zhanghailiang@huawei.com>

* Wen Congyang (wency@cn.fujitsu.com) wrote:
> On 04/24/2015 03:47 PM, Paolo Bonzini wrote:
> > 
> > 
> > On 24/04/2015 04:16, Wen Congyang wrote:
> >>>>>> I think the primary shouldn't do any I/O after failover (and the
> >>>>>> secondary should close the NBD server) so it is probably okay to ignore
> >>>>>> the removal for now.  Inserting the filter dynamically is probably
> >>>>>> needed though.
> >>>>
> >>>> Or maybe just enabling/disabling?
> >> Hmm, after failover, the secondary qemu should become primary qemu, but we don't
> >> know the nbd server's IP/port when we execute the secondary qemu. So we need
> >> to inserting nbd client dynamically after failover.
> > 
> > True, but secondary->primary switch is already not supported in v3.
> 
> Yes, we should consider it, and support it more easily later.
> 
> If we can add a filter dynamically, we can add a filter that's file is nbd
> dynamically after secondary qemu's nbd server is ready. In this case, I think
> there is no need to touch nbd client.

Yes, I think maybe the harder part is getting a copy of the current disk
contents to the new secondary while the new primary is still running.

Dave

> 
> Thanks
> Wen Congyang
> 
> > 
> > Kevin/Stefan, is there a design document somewhere that covers at least
> > static filters?
> > 
> > Paolo
> > .
> > 
> 
--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK