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

[Alberto Garcia]

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?

Berto