Re: [Qemu-devel] [RFC PATCH 01/14] docs: block replication's description

[Paolo Bonzini]

On 16/03/2015 07:19, Wen Congyang wrote:
> On 03/13/2015 05:05 PM, Fam Zheng wrote:
>> On Fri, 03/13 17:01, Wen Congyang wrote:
>>> On 03/11/2015 02:49 PM, Fam Zheng wrote:
>>>> On Wed, 03/11 14:44, Wen Congyang wrote:
>>>>> On 03/03/2015 03:59 PM, Fam Zheng wrote:
>>>>>> On Tue, 03/03 15:53, Wen Congyang wrote:
>>>>>>> I test qcow2_make_empty()'s performance. The result shows that it may
>>>>>>> take about 100ms(normal sata disk). It is not acceptable for COLO. So
>>>>>>> I think disk buff is necessary(just use it to replace qcow2).
>>>>>>
>>>>>> Why not tmpfs or ramdisk?
>>>>>
>>>>> Another problem:
>>>>> After failover, secondary write request will be written in (active disk)?
>>>>> It is better to write request to (nbd target). Is there any feature can
>>>>> be reused to implement it?
>>>>
>>>> You can use block commit or stream to move the data.
>>>
>>> Can the job stream move the data? I don't find the write ops in 
>>> block/stream.c.
>>
>> It is bdrv_co_copy_on_readv that moves data.
> 
> Does the job stream move the data from base to top?

Yes.  block-commit goes in the other direction.

Paolo