Wen Congyang <[email protected]> wrote:
> On 03/27/2015 05:57 PM, Stefan Hajnoczi wrote:
>>>> You must use -drive cache=none if you want to use live migration. It
>>>> should not directly affect memory during migration though.
>>>
>>> Otherwise, what will happen? If the user doesn't use cache=none, and
>>> tries to use live migration, qemu doesn't output any message or trigger
>>> an event to notify the user.
>>
>> There is a risk that the destination host sees an inconsistent view of
>> the image file because the source was still accessing it towards the
>> end of migration.
>
> Does the flag BDRV_O_NOFLUSH cause it?
The biggest isue is reads.
Target: reads 1st block of disk
it enters page cache of target
Source: reads and writes lots of blocks
Migration happens.
Target: rereads 1st block of disk, and gets stalled contents.
No amount of fdatasync(), syncs() whatever on source will fix this problem.
Later, Juan.
