[openstack-dev] [nova] volume affinity filter for nova scheduler

Álvaro López García alvaro.lopez.garcia at cern.ch
Thu Jul 11 07:12:25 UTC 2013

On Wed 10 Jul 2013 (13:10), Joe Gordon wrote:
> On Mon, Jul 8, 2013 at 8:53 AM, Ilya Kharin <ikharin at mirantis.com> wrote:
> > Hi all.
> >
> > In my opinion it is about things that can live in one form or another,
> > because
> > in some cases there is a need to place an instance in the same place where
> > its
> > block device is located or will be attached. Both solutions that let you
> > do it,
> > I mean filter and weigher, have a right to life. A lot depends on the
> > requirements that are present when you start an instance:
> >
> > 1.  In the case when you want to put them together preferably, there
> > should be
> >     a weigher. If that fails, then the user should not worry about it, the
> >     instance will be started though not as optimally as wanted.
> > 2.  When it is important that they are together and nothing else is
> > acceptable,
> >     then there should be a filter. Some applications that are built on top
> > of
> >     OpenStack may require that instance must be together with a particular
> >     volume.
> >
> I question how 'cloudy' an architecture that *requires* instances and
> volumes be on the same node.  If we treat instances as ephemeral and
> volumes as persistent having them live on the same node is a contradiction.

I do fully agree with this. In the worst case, a machine requiring
affinity with a volume that is stored in a compute-node without enough
room will never boot.

Álvaro López García                              aloga at ifca.unican.es
Instituto de Física de Cantabria         http://alvarolopez.github.io
Ed. Juan Jordá, Campus UC                      tel: (+34) 942 200 969
Avda. de los Castros s/n
39005 Santander (SPAIN)
"Those that can, do. Those that can't, complain." -- Linus Torvalds

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