Re: qemu and qemu.git -> Migration + disk stress introduces qcow2 corruptions

[Avi Kivity <avi@redhat.com>]

On 11/12/2011 03:30 PM, Anthony Liguori wrote:
>> Nor can you yank support for migration this way.  Might as well put a
>> big sign on 1.0, "Do Not Use This Release".
>
>
> You're joking, right?

No.

>
> Let's be very clear.  Live migration works perfectly fine when you use
> raw images and coherent shared storage.

This is not a realistic setup.

>
> NFS is *not* fully coherent so in order to do live migration with NFS,
> you have to use cache=none.

While putting restrictions on features is not ideal, requiring
cache=none is acceptable as it's that's what's recommended anyway by the
qemu management tool writer's guide.

>
> Live migration does not work with image formats.  There's not a simple
> way to make it support image files.  So far, no one has put the work
> into making it support image files.

It must be possible, since RHEL's qemu-kvm supports it.  I'm sure Kevin
and Juan can make it work.

>
>>
>> Making formal plans and sticking to them is great, but not to the point
>> of ignoring reality.
>
> Why do you think this is an end of the world feature?
>

In 2007 when live migration was added, random restrictions like that
weren't important.  4.5 years later, pulling support for it makes us
look like a joke.  Even if it's not technically a regression, in terms
of user's expectations, it is.  It's simply impossible to delay it for
six more months, or however long the 1.1 cycle takes.

-- 
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.