On Wed, Oct 12, 2016 at 7:10 AM, Giulio Fidente <gfide...@redhat.com> wrote:
> hi,
>
> we introduced support for the deployment of Ceph in the liberty release so
> that it could optionally be used as backend for one or more of Cinder,
> Glance, Nova and more recently Gnocchi.
>
> We used to deploy Ceph MONs on the controller nodes and Ceph OSDs on
> dedicated ceph-storage nodes so a deployment of OpenStack with Ceph would
> need at least 1 more additional node to host a Ceph OSD.
>
> In our HA scenario the storage backends are configured as follows:
>
> Glance -> Swift
> Nova (ephemeral) -> Local
> Cinder (persistent) -> LVM (on controllers)
> Gnocchi -> Swift
>
> The downside of the above configuration is that Cinder volumes can not be
> replicated across the controller nodes and become unavailable if a
> controller fails, while production environments generally expect persistent
> storage to be highly available. Cinder volumes instead could even get lost
> completely in case of a permanent failure of a controller.
>
> With the Newton release and the composable roles we can now deploy Ceph OSDs
> on the compute nodes, removing the requirement we had for an additional node
> to host a Ceph OSD.
>
> I would like to ask for some feedback on the possibility of deploying Ceph
> by default in the HA scenario and use it as backend for Cinder.
>
> Also using Swift as backend for Glance and Gnocchi is enough to cover the
> availability issue for the data, but it also means we're storing that data
> on the controller nodes which might or might not be wanted; I don't see a
> strong reason for defaulting them to Ceph, but it might make more sense when
> Ceph is available; feedback about this would be appreciated as well.
>
> Finally a shared backend (Ceph) for Nova would allow live migrations but
> probably decrease performances for the guests in general; so I'd be against
> defaulting Nova to Ceph. Feedback?

+1 on making ceph default backend for nova/glance/cinder/gnocchi.
I think this is the most common use-case we currently have in our
deployments AFIK.

Also, I'll continue to work on scenarios jobs (scenario002 and
scenario003 without Ceph to cover other use cases).

> --
> Giulio Fidente
> GPG KEY: 08D733BA
>
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-- 
Emilien Macchi

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