We are using a production cluster which started in Firefly, then moved to
Giant, Hammer and finally Jewel. So our images have different features
correspondind to the value of "rbd_default_features" of the version when
they were created.
We have actually three pack of features activated :
image with :
- layering ~ 1
- layering, striping ~3
- layering, exclusive-lock, object-map, fast-diff, deep-flatten ~ 61

1) Is it a good idea to try to give all images the same features ?
2) Is it possible to disable the striping feature on an already created
image (we never specify any stripe-unit nor stripe-count) ?
3) What is the behaviour of an already created image on which we activate
the object-map feature ? Will a process try to rebuild a index of used
blocks - if no, if we delete later the image, will ceph try to remove all
the blocks or only the blocks refered by object-map index ?
4) We are on Jewel but with tunables set to hammer (Centos 7.2). What are
the best default features to set in that case ? (we use Ceph  under an
Openstack for glance, nova and cinder
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