Description of problem:

OSP-d should support multiple same type Cinder backends. 

Use case 1: You would like to use 2 external Ceph pools as rbd backend. Each pool uses different type of drives (HDD and SSD) for providing different type of storage QoS for the Cinder volumes.

Use case 2: You are using a NFS server for storing the Cinder volumes and it runs out of storage capacity. You want to scale out by adding an additional NFS storage server where to store future Cinder volumes.