You can achieve this manually by following the steps outlined here: https://medium.com/@michaelgugino/deploying-cinder-with-multiple-ceph-cluster-backends-2cd90d64b10 (https://medium.com/@michaelgugino/dep...)
You can also automate this process with OpenStack-Ansible (Newton and later):
http://docs.openstack.org/developer/openstack-ansible-ceph_client/configure-ceph.html#extra-client-configuration-files (http://docs.openstack.org/developer/o...)
Synopsis:
Cinder needs configuration for the new backend to point to a different ceph.conf file (ie, /etc/ceph/ceph-new.conf).
/etc/ceph/ceph-new.conf must specify a keyfile directly
The username for each ceph client user must be unique across clusters (ie, cinder, cinder2)
A new secret-uuid is used to define a new libvirt secret (along with new client name and appropriate key), and is provided to cinder.conf
If you're not using authentication, you can most likely just provide the additional ceph.conf file to cinder.