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Date: Tue, 23 Jun 2015 21:54:04 +0800
From: Wen Congyang <ghostwcy@gmail.com>
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Subject: Re: [Qemu-devel] [Qemu-block] [PATCH COLO-Block v6 07/16] Add new
 block driver interface to connect/disconnect the remote target
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To: Stefan Hajnoczi <stefanha@redhat.com>
Cc: Kevin Wolf <kwolf@redhat.com>, Fam Zheng <famz@redhat.com>, Lai Jiangshan <laijs@cn.fujitsu.com>, qemu block <qemu-block@nongnu.org>, Stefan Hajnoczi <stefanha@gmail.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>, Paolo Bonzini <pbonzini@redhat.com>, Yang Hongyang <yanghy@cn.fujitsu.com>, "Dr. David Alan Gilbert" <dgilbert@redhat.com>, zhanghailiang <zhang.zhanghailiang@huawei.com>

At 2015/6/23 21:42, Stefan Hajnoczi Wrote:
> On Mon, Jun 22, 2015 at 09:56:24PM +0800, Wen Congyang wrote:
>>> The NBD connect should not be performed during downtime, regardless of
>>> whether a monitor command is used or not.
>>
>> Why?
>
> NBD connection establishment takes unbounded time.  It can extend the
> downtime period and cause users to notice that the guest is unavailable.
>
> The point of COLO is fault tolerance and high availability.  In order to
> achieve that, COLO must minimize downtime.  If an operation can be
> performed outside the migration downtime phase, then it should be done
> outside.

Yes, you are right. I will think about it.

Thanks
Wen Congyang

>
> Stefan
>