Storage is found in many parts of the OpenStack cloud environment. It is important to understand the distinction between ephemeral storage and persistent storage:
Ephemeral storage - If you only deploy OpenStack Compute service (nova), by default your users do not have access to any form of persistent storage. The disks associated with VMs are ephemeral, meaning that from the user’s point of view they disappear when a virtual machine is terminated.
Persistent storage - Persistent storage means that the storage resource outlives any other resource and is always available, regardless of the state of a running instance.
OpenStack clouds explicitly support three types of persistent storage: Object Storage, Block Storage, and File-based storage.
Hope this will help.