How to do it...

1. Both clients must have the rbd-mirror installed and running:

        # yum install rbd-mirror
        # systemctl enable ceph-rbd-mirror.target
        # systemctl enable ceph-rbd-mirror@<client-id>
        # systemctl start ceph-rbd-mirror@<client-id>

1. As with one way mirroring, both clients must have copies of the respective cluster configuration files and keyrings for client users for the mirrored pools.
2. The pools to be replicated must have mirroring enabled at the pool or image level in both clusters:

        # rbd mirror pool enable <pool> <replication type>
        # rbd mirror pool enable <pool> <replication type>

1. Validate that mirroring has been successfully enabled:

        # rbd mirror pool status data

1. The pools to be replicated must have a peer registered for mirroring in both clusters:

       # rbd mirror pool peer add <pool> 
         client.<user>@<primary cluster name>
       # rbd mirror pool peer add <pool> 
         client.<user>@<secondary cluster name>