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Hi Michal,

Thank you for explaining!
I could understand the mechanism of cinder-backup.

> 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.
Sure.
But, according to your explanation, my assumptions won't be realized.

On 2017/01/20 17:31, Dulko, Michal wrote:
> 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
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