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On Jan 16, 2014, at 9:41 PM, Jiang, Yunhong <yunhong.jiang at intel.com> wrote:

> I noticed the BP has been approved, but I really want to understand more on the reason, can anyone provide me some hints?
>  
> In the BP, it states that “For resize, we need to confirm, as we want to give end user an opportunity to rollback”. But why do we want to give user an opportunity to rollback to resize? And why that reason does not apply to cold migration and live migration?

The confirm is so the user can verify that the instance is still functional in the new state. We leave the old instance around so they can abort and return to the old instance if something goes wrong. This could apply to cold migration as well since it uses the same code paths, but it definitely does not make sense in the case of live-migration, because there is no old vm to revert to.

In the case of cold migration, the state is quite confusing as “RESIZE_VERIFY”, and the need to confirm is not immediately obvious so I think that is driving the change.

Vish

>  
> Thanks
> --jyh
>  
> From: Jay Lau [mailto:jay.lau.513 at gmail.com] 
> Sent: Thursday, January 16, 2014 3:27 PM
> To: OpenStack Development Mailing List (not for usage questions)
> Subject: Re: [openstack-dev] [Nova] why don't we deal with "claims" when live migrating an instance?
>  
> Hi Scott,
> 
> I'm now trying to fix this issue at https://blueprints.launchpad.net/nova/+spec/auto-confirm-cold-migration
> 
> After the fix, we do not need to "confirm" the cold migration.
> 
> http://lists.openstack.org/pipermail/openstack-dev/2014-January/023726.html
> 
> Thanks,
> 
> Jay
>  
> 
> 2014/1/17 Scott Devoid <devoid at anl.gov>
> Related question: Why does resize get called (and the VM put in "RESIZE VERIFY" state) when migrating from one machine to another, keeping the same flavor?
>  
> 
> On Thu, Jan 16, 2014 at 9:54 AM, Brian Elliott <bdelliott at gmail.com> wrote:
> 
> On Jan 15, 2014, at 4:34 PM, Clint Byrum <clint at fewbar.com> wrote:
> 
> > Hi Chris. Your thread may have gone unnoticed as it lacked the Nova tag.
> > I've added it to the subject of this reply... that might attract them.  :)
> >
> > Excerpts from Chris Friesen's message of 2014-01-15 12:32:36 -0800:
> >> When we create a new instance via _build_instance() or
> >> _build_and_run_instance(), in both cases we call instance_claim() to
> >> reserve and test for resources.
> >>
> >> During a cold migration I see us calling prep_resize() which calls
> >> resize_claim().
> >>
> >> How come we don't need to do something like this when we live migrate an
> >> instance?  Do we track the hypervisor overhead somewhere in the instance?
> >>
> >> Chris
> >>
> 
> It is a good point and it should be done.  It is effectively a bug.
> 
> Brian
> 
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