The OpenStack stack uses the following storage types:

Storage types

On-instance / ephemeral	Volumes block storage (Cinder)	Object Storage (Swift)
Runs operating systems and provides scratch space	Used for adding additional persistent storage to a virtual machine (VM)	Used for storing virtual machine images and data
Persists until VM is terminated	Persists until deleted	Persists until deleted
Access associated with a VM	Access associated with a VM	Available from anywhere
Implemented as a filesystem underlying OpenStack Compute	Mounted via OpenStack Block-Storage controlled protocol (for example, iSCSI)	REST API
Administrator configures size setting, based on flavors	Sizings based on need	Easily scalable for future growth
Example: 10GB first disk, 30GB/core second disk	Example: 1TB "extra hard drive"	Example: 10s of TBs of data set storage

Other points of note include: OpenStack Object Storage is not used like a traditional hard drive. Object storage is all about relaxing some of the constraints of a POSIX-style file system. The access to it is API-based (and the API uses http). This is a good idea as if you don't have to provide atomic operations (that is, you can rely on eventual consistency), you can much more easily scale a storage system and avoid a central point of failure. The OpenStack Image Service is used to manage the virtual machine images in an OpenStack cluster, not store them. Instead, it provides an abstraction to different methods for storage - a bridge to the storage, not the storage itself. OpenStack Object Storage can function on its own. The Object Storage (swift) product can be used independently of the Compute (nova) product.