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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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