Open Stack

Without the mentioned qemu change the live migration is still fully
functional with volume backed instances just like on x86 hosts, with
the following caveat: The safety check whether the target host CPU is
compatible with the source host CPU is not performed. Therefore, it is
a responsibility of the OpenStack admin triggering the migration to
make sure they are compatible. An example of such an incompatibility
is where the target machine is an older generation than the source
machine, and the guest is using features of the newer machine that are
not available on the older machine.

For OpenStack with System z we think this behavior is acceptable, because
we assume that the typical OpenStack with System z cloud will be a private 

one where the OpenStack admin is the same person as the System z admin,
or at least in close contact. These admins know their environment very
well. So we think that this caveat would not prevent any customer from
using live migration on System z.

As you may have noticed I changed the logging from warning to debug.
I'm a bit conflicted between these two possibilities. What's your 
opinion on that?

Regards,
Markus Zoeller (markus_z)

Michael Still <mikal at stillhq.com> wrote on 04/08/2015 12:33:40 AM:

> From: Michael Still <mikal at stillhq.com>
> To: "OpenStack Development Mailing List (not for usage questions)" 
> <openstack-dev at lists.openstack.org>
> Date: 04/08/2015 12:39 AM
> Subject: Re: [openstack-dev] [nova] [stringfreeze] request for SFE for
> live-migration on system z (review 166130)
> 
> How many users are likely to use live migration without the changes to
> qemu you mention? How functional would the live migration be?
> 
> Thanks,
> Michael
> 
> On Wed, Apr 8, 2015 at 2:45 AM, Markus Zoeller <mzoeller at de.ibm.com> 
wrote:
> > I'd like to request a string freeze exception for this review:
> >
> >     https://review.openstack.org/#/c/166130/
> >
> > Justification:
> > This fix would enable the live-migration on the system z platform. 
This
> > platform (arch=s390x) doesn't currently support the CPU comparison but
> > is working on patch sets in qemu to enable this [1]. With the patch 
set
> > above a customer would at least have the possibility to use the live-
> > migration feature with Kilo on system z.
> >
> > [1] http://lists.gnu.org/archive/html/qemu-devel/2014-05/msg04296.html
> >
> >
> > 
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> 
> 
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> Rackspace Australia
> 
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