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Except your failure domain includes the cinder volume service, independent
of the resiliency of you backend, so if they're all on one node then you
don't really have availability zones.

I have historically strongly espoused the same view as Ben, though there
are lots of people who want fake availability zones... No strong use cases
though
On 28 Aug 2015 11:59, "Dulko, Michal" <michal.dulko at intel.com> wrote:

> > From: Ben Swartzlander [mailto:ben at swartzlander.org]
> > Sent: Thursday, August 27, 2015 8:11 PM
> > To: OpenStack Development Mailing List (not for usage questions)
> >
> > On 08/27/2015 10:43 AM, Ivan Kolodyazhny wrote:
> >
> >
> >       Hi,
> >
> >       Looks like we need to be able to set AZ per backend. What do you
> > think about such option?
> >
> >
> >
> > I dislike such an option.
> >
> > The whole premise behind an AZ is that it's a failure domain. The node
> > running the cinder services is in exactly one such failure domain. If
> you have 2
> > backends in 2 different AZs, then the cinder services managing those
> > backends should be running on nodes that are also in those AZs. If you
> do it
> > any other way then you create a situation where a failure in one AZ
> causes
> > loss of services in a different AZ, which is exactly what the AZ feature
> is trying
> > to avoid.
> >
> > If you do the correct thing and run cinder services on nodes in the AZs
> that
> > they're managing then you will never have a problem with the one-AZ-per-
> > cinder.conf design we have today.
> >
> > -Ben
>
> I disagree. You may have failure domains done on a different level, like
> using Ceph mechanisms for that. In such case you want to provide the user
> with a single backend regardless of compute AZ partitioning. To address
> such needs you would need to set multiple AZ per backend to make this
> achievable.
>
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