[openstack-dev] [cinder][nova] Proper behavior for os-force_detach

Gorka Eguileor geguileo at redhat.com
Wed Jul 18 09:02:27 UTC 2018

On 17/07, Sean McGinnis wrote:
> On Tue, Jul 17, 2018 at 04:06:29PM -0300, Erlon Cruz wrote:
> > Hi Cinder and Nova folks,
> >
> > Working on some tests for our drivers, I stumbled upon this tempest test
> > 'force_detach_volume'
> > that is calling Cinder API passing a 'None' connector. At the time this was
> > added several CIs
> > went down, and people started discussing whether this (accepting/sending a
> > None connector)
> > would be the proper behavior for what is expected to a driver to do[1]. So,
> > some of CIs started
> > just skipping that test[2][3][4] and others implemented fixes that made the
> > driver to disconnected
> > the volume from all hosts if a None connector was received[5][6][7].
> Right, it was determined the correct behavior for this was to disconnect the
> volume from all hosts. The CIs that are skipping this test should stop doing so
> (once their drivers are fixed of course).
> >
> > While implementing this fix seems to be straightforward, I feel that just
> > removing the volume
> > from all hosts is not the correct thing to do mainly considering that we
> > can have multi-attach.
> >
> I don't think multiattach makes a difference here. Someone is forcibly
> detaching the volume and not specifying an individual connection. So based on
> that, Cinder should be removing any connections, whether that is to one or
> several hosts.


I agree with Sean, drivers should remove all connections for the volume.

Even without multiattach there are cases where you'll have multiple
connections for the same volume, like in a Live Migration.

It's also very useful when Nova and Cinder get out of sync and your
volume has leftover connections. In this case if you try to delete the
volume you get a "volume in use" error from some drivers.


> > So, my questions are: What is the best way to fix this problem? Should
> > Cinder API continue to
> > accept detachments with None connectors? If, so, what would be the effects
> > on other Nova
> > attachments for the same volume? Is there any side effect if the volume is
> > not multi-attached?
> >
> > Additionally to this thread here, I should bring this topic to tomorrow's
> > Cinder's meeting,
> > so please join if you have something to share.
> >
> +1 - good plan.
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