Hi,

I've configured multi-backend for the cinder accordingly to the https://ceph.com/geen-categorie/ceph-and-cinder-multi-backend/ (article) Everything works correctly (volumes are created on the correct rbd pool), except one small thing - cinder creates volume with all supported by ceph image-features, which makes us unable to map rbd drives.

We've already had rbd_default_features = 3 in /etc/ceph/ceph.conf and cinder had been creating volumes correctly before configuration of multi-backend.

This volume was created before multi-backend configuration:

root@openstack-sandbox:~# rbd info volumes/volume-2c168404-3cc9-40fe-9737-2e68bd1caeed
rbd image 'volume-2c168404-3cc9-40fe-9737-2e68bd1caeed':
        size 20480 MB in 5120 objects
        order 22 (4096 kB objects)
        block_name_prefix: rbd_data.856e51572de970
        format: 2
        features: layering
        flags: 
        create_timestamp: Thu Mar  1 21:17:56 2018
root@openstack-sandbox:~#

And this volume almost right after:

root@openstack-sandbox:~# rbd info volumes/volume-a8d66fb5-de3a-4b7b-9a23-453ee6cfa334
rbd image 'volume-a8d66fb5-de3a-4b7b-9a23-453ee6cfa334':
        size 10240 MB in 2560 objects
        order 22 (4096 kB objects)
        block_name_prefix: rbd_data.bfdeae4679ac77
        format: 2
        features: layering, exclusive-lock, object-map, fast-diff, deep-flatten
        flags: 
        create_timestamp: Thu Mar 22 17:29:45 2018
root@openstack-sandbox:~#

If I'm creating rbd drive manually, without providing any additional options, it's created only with layering feature.

So the question is - how to provide either custom flags for volume creation in ceph to cinder or specify required features?

I suppose, that some options may be provided as the property for volume type, like volume_backend_name, but I haven't found anything related in the documentation.