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On Tue, Sep 15, 2015 at 8:04 AM, Eduard Matei <
eduard.matei at cloudfounders.com> wrote:

> Hi,
>
> This all started when we were testing Evacuate with our storage driver.
> We thought we found a bug (https://bugs.launchpad.net/cinder/+bug/1491276)
> then Scott replied that we should be running cinder-volume service separate
> from nova-compute.
> For some internal reasons we can't do that - yet, but we have some
> questions regarding the behavior of the service:
>
> - on our original test setup we have 3 nodes (1 controller + compute +
> cinder, 2 compute + cinder).
> -- when we shutdown the second node and tried to evacuate, the call was
> routed to cinder-volume of the halted node instead of going to other nodes
> (there were still 2 cinder-volume services up) - WHY?
> - on the new planned setup we will have 6 nodes (3 dedicated controller +
> cinder-volume, 3 compute)
> -- in this case which cinder-volume will manage which volume on which
> compute node?
> -- what if: one compute node and one controller go down - will the
> Evacuate still work if one of the cinder-volume services is down? How can
> we tell - for sure - that this setup will work in case ANY 1 controller and
> 1 compute nodes go down?
>
> Hypothetical:
> - if 3 dedicated controller + cinder-volume nodes work can perform
> evacuate when one of them is down (at the same time with one compute), WHY
> can't the same 3 nodes perform evacuate when compute services is running on
> the same nodes (so 1 cinder is down and 1 compute)
> - if the answer to above question is "They can't " then what is the
> purpose of running 3 cinder-volume services if they can't handle one
> failure?
> - and if the answer to above question is "You only run one cinder-volume"
> then how can it handle failure of controller node?
>
> Thanks,
>
> Eduard
>
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> ​Not sure I follow all your permutations and things here.  But... one
common misconception about multiple c-vol services;  The act of just
"deploying multiple c-vols" doesn't mean you get any sort of HA or
failover.  The default/base case for multiple c-vols is actually just for
scale out and that's it.

If you want to actually do things like have them fail over you have to look
at configuring the c-vol services with virtual-ips and using the same name
for each service etc.  In other words, do a true HA deployment.

Maybe I'm not following here but it sounds like maybe you have the wrong
expectations around what multiple c-vol services buys you.  ​
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