Comment 3 for bug 1704201

> I also notice that the only time the read only tag is followed is when it is set in the cinder table: volume_admin_metadata. If it is set in the volume_metadata table it is ignored.

That's because that is where the API code puts the metadata value:

https://github.com/openstack/cinder/blob/1d31f244c86e2610e19d5d4a2a868f81d52296f4/cinder/volume/api.py#L1608