[cinder] ceph multiattach details?

Sean McGinnis sean.mcginnis at gmx.com
Tue May 28 13:33:23 UTC 2019

On Tue, May 28, 2019 at 08:57:17AM -0400, Erik McCormick wrote:
> On Tue, May 28, 2019, 8:29 AM Bernd Bausch <berndbausch at gmail.com> wrote:
> > Thanks for clarifying this Erik. Let me point out then that the release
> > notes [1] are worded rather unequivocally, and what you are saying
> > contradicts them:
> >
> > RBD driver has added multiattach support. It should be noted that
> > replication and multiattach are mutually exclusive, so a single RBD volume
> > can only be configured to support one of these features at a time.
> > Additionally, RBD image features are not preserved which prevents a volume
> > being retyped from multiattach to another type. This limitation is
> > temporary and will be addressed soon.
> >
> > Bernd.
> >
> I haven't even looked at Stein yet so I could be wrong,  but I thin this is
> referring to replication like RBD mirroring. There's still an issue in
> Ceph, as far as I know, where ceph's object replication would have a
> problem with multi-attach. I haven't come across any Ceph release note to
> say this has been addressed.
> Hopefully someone from the Cinder team can straighten us out.
> -Erik

Multiattach support has indeed been enabled for RBD as of the Stein release.
Though there are the known caveats that you point out.

I thought there was a pending patch to add some details on this to to the RBD
driver configuration reference, but I am not finding anything at the moment.

I don't have all the details on that myself, but hopefully one of the RBD
driver maintainers can chime in here with better details.


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