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Re: [Qemu-block] [PATCH v9 2/3] quorum: implement bdrv_add_child() and b

From: Wen Congyang
Subject: Re: [Qemu-block] [PATCH v9 2/3] quorum: implement bdrv_add_child() and bdrv_del_child()
Date: Mon, 25 Jan 2016 09:13:58 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.5.0

On 01/23/2016 04:02 AM, Dr. David Alan Gilbert wrote:
> * Alberto Garcia (address@hidden) wrote:
>> On Thu 21 Jan 2016 05:58:42 PM CET, Eric Blake <address@hidden> wrote:
>>>>>> In general, what do you do to make sure that the data in a new Quorum
>>>>>> child is consistent with that of the rest of the array?
>>>>> Quorum can have more than one child when it starts. But we don't do
>>>>> the similar check. So I don't think we should do such check here.
>>>> Yes, but when you start a VM you can verify in advance that all
>>>> members of the Quorum have the same data. If you do that on a running
>>>> VM how can you know if the new disk is consistent with the others?
>>> User error if it is not.  Just the same as it is user error if you
>>> request a shallow drive-mirror but the destination is not the same
>>> contents as the backing file.  I don't think qemu has to protect us
>>> from user error in this case.
>> But the backing file is read-only so the user can guarantee that the
>> destination has the same data before the shallow mirror. How do you do
>> that in this case?
> I think in the colo case they're relying on doing a block migrate
> to synchronise the remote disk prior to switching into colo mode.

Yes, we can do a block migration to sync the disk. After the migration finished,
we stop block migration before starting colo.

Wen Congyang

> Dave
>> Berto
> --
> Dr. David Alan Gilbert / address@hidden / Manchester, UK
> .

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