[cinder] ceph multiattach details?

Erik McCormick emccormick at cirrusseven.com
Tue May 28 02:30:04 UTC 2019

On Mon, May 27, 2019, 5:33 PM Martinx - ジェームズ <thiagocmartinsc at gmail.com>

> Hello,
>  I'm very curious about this as well!
>  It would be awesome to support Cinder multi-attach when using Ceph... If
> the code is already there, how to use it?!
> Cheers,
> Thiago
> On Mon, 27 May 2019 at 03:52, Bernd Bausch <berndbausch at gmail.com> wrote:
>> The Stein release notes mention that the RBD driver now supports
>> multiattach, but i have not found any details. Are there limitations? Is
>> there a need to configure anything?
>> In the RBD driver
>> <https://opendev.org/openstack/cinder/src/branch/master/cinder/volume/drivers/rbd.py#L767>,
>> I find this:
>>     def _enable_multiattach(self, volume):
>>         multipath_feature_exclusions = [
>>             self.rbd.RBD_FEATURE_JOURNALING,
>>             self.rbd.RBD_FEATURE_FAST_DIFF,
>>             self.rbd.RBD_FEATURE_OBJECT_MAP,
>>             self.rbd.RBD_FEATURE_EXCLUSIVE_LOCK,
>>         ]
>> This seems to mean that journaling and other features (to me, it's not
>> quite clear what they are) will be automatically disabled when switching on
>> multiattachment.
>> Further down in the code I see that replication and multiattach are
>> mutually exclusive.
>> Is there some documentation about the Ceph multiattach feature, even an
>> email thread?
>> Thanks,
>> Bernd
There isn't really a Ceph multi-attach feature using Cinder. The code
comment is stating that, while the Openstack side of things is in place,
Ceph doesn't yet support it with RBD due to replication issues with
multiple clients. The Ceph community is aware of it, but has thus far
focused on CephFS as the shared file system instead.

This could possibly be used with the NFS Cinder driver talking to Ganesha
with CephFS mounted. You may also want to look at Openstack's Manilla
project to orchestrate that.


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