openstack-manuals/doc/common-rst/get_started_storage_concepts.rst

Storage concepts

The OpenStack stack uses the following storage types:

Storage types

On-instance / ephemeral	Block storage (cinder)	Object Storage (swift)	File Storage (manila)
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	Used for providing file shares to a virtual machine
Persists until VM is terminated	Persists until deleted	Persists until deleted	Persists until deleted
Access associated with a VM	Access associated with a VM	Available from anywhere	Access can be provided to a VM
Implemented as a filesystem underlying OpenStack Compute	Mounted via OpenStack Block Storage controlled protocol (for example, iSCSI)	REST API	Provides Shared File System service via nfs, cifs, glusterfs, or hdfs protocol
Encryption is available	Encryption is available	Work in progress - expected for the Mitaka release	Encryption is not available yet
Administrator configures size setting, based on flavors	Sizings based on need	Easily scalable for future growth	Sizing based on need
Example: 10 GB first disk, 30 GB/core second disk	Example: 1 TB "extra hard drive"	Example: 10s of TBs of data set storage	Example: 1 TB of file share

Note

• You cannot use OpenStack Object Storage like a traditional hard drive. The Object Storage relaxes some of the constraints of a POSIX-style file system to get other gains. You can access the objects through an API which uses HTTP. Subsequently you don't have to provide atomic operations (that is, relying on eventual consistency), you can scale a storage system easily 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. It provides an abstraction to different methods for storage - a bridge to the storage, not the storage itself.
• The OpenStack Object Storage can function on its own. The Object Storage (swift) product can be used independently of the Compute (nova) product.