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On Fri, 2017-01-20 at 14:15 +0900, Rikimaru Honjo wrote:
> Hi Cinder devs,
> 
> I have a question about cinder.
> Can I run cinder-volume and cinder-backup on a same host when I using
> iscsi backend?
> 
> I afraid that iscsi operations will be conflicted between cinder-
> volume and cinder-backup.
> In my understanding, iscsi operations are serialized for each
> individual process.
> But these could be raced between processes.
> 
> e.g.(Caution: This is just a forecast.)
> If cinder-backup execute "multipath -r" while cinder-volume is
> terminating connection,
> a multipath garbage will remain unexpectedly.

Hi,

Before Mitaka it was *required* to place cinder-volume and cinder-
backup on the same node. As both services shared same file lock
directory, it was safe. In fact cinder-backup simply imported cinder-
volume code.

Since Mitaka cinder-backup doesn't do any iSCSI operations directly and
attaches volumes by calling cinder-volume over RPC. This means that
it's possible to place cinder-backup on other node than cinder-volume,
but it's still totally safe to place them together.

If you're able to reproduce a scenario that fails these assumptions,
please file a bug report and we'll be happy to investigate and provide
a fix.

Thanks,
Michal