OpenStack Storage Design Mode

Table 5.1. OpenStack Storage

	Ephemeral storage	Block storage	Object storage
Used to…	Run operating system and scratch space	Add additional persistent storage to a virtual machine (VM)	Store data, including VM images
Accessed through…	A file system	A block device that can be partitioned, formatted and mounted (such as, /dev/vdc)	REST API
Accessible from…	Within a VM	Within a VM	Anywhere
Managed by…	OpenStack Compute (Nova)	OpenStack Block Storage (Cinder)	OpenStack Object Storage (Swift)
Persists until…	VM is terminated	Deleted by user	Deleted by user
Sizing determined by…	Administrator configures size settings, known as flavors	Specified by user in initial request	Amount of available physical storage
Example of typical usage…	10 GB first disk, 30GB second disk	1 TB disk	10s of TBs of dataset storage

If you only deploy the OpenStack Compute Service (nova), your users do not have access to any form of persistent storage by default. The disks associated with VMs are "ephemeral", meaning that (from the user's point of view) they effectively disappear when a virtual machine is terminated. You must identify what type of persistent storage you want to support for your users.

Today, OpenStack clouds explicitly support two types of persistent storage: object storage and block storage.

 Object Storage

With object storage, users access binary objects through a REST API. You may be familiar with Amazon S3, which is a well-known example of an object storage system. If your intended users need to archive or manage large datasets, you want to provide them with object storage. In addition, OpenStack can store your virtual machine (VM) images inside of an object storage system, as an alternative to storing the images on a file system.