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Date: Fri, 24 Apr 2015 15:55:46 +0800
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Subject: Re: [Qemu-devel] [PATCH COLO v3 01/14] docs: block replication's
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To: Paolo Bonzini <pbonzini@redhat.com>, Fam Zheng <famz@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Yang Hongyang <yanghy@cn.fujitsu.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>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, qemu devel <qemu-devel@nongnu.org>, Gonglei <arei.gonglei@huawei.com>, Stefan Hajnoczi <stefanha@redhat.com>, Max Reitz <mreitz@redhat.com>, zhanghailiang <zhang.zhanghailiang@huawei.com>

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.

Thanks
Wen Congyang

> 
> Kevin/Stefan, is there a design document somewhere that covers at least
> static filters?
> 
> Paolo
> .
>