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

[Alberto Garcia]

On Thu 21 Jan 2016 02:54:10 AM CET, Wen Congyang <address@hidden> wrote:

>>> @@ -875,9 +878,9 @@ static int quorum_open(BlockDriverState *bs, QDict 
>>> *options, int flags,
>>>          ret = -EINVAL;
>>>          goto exit;
>>>      }
>>> -    if (s->num_children < 2) {
>>> +    if (s->num_children < 1) {
>>>          error_setg(&local_err,
>>> -                   "Number of provided children must be greater than 1");
>>> +                   "Number of provided children must be 1 or more");
>>>          ret = -EINVAL;
>>>          goto exit;
>>>      }
>> 
>> I have a question: if you have a Quorum with just one member and you
>> add a new one, how do you know if it has the same data as the
>> existing one?
>> 
>> 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?

Berto