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Storage concepts
The OpenStack stack uses the following storage types:
| On-instance / ephemeral | 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 |
| Encryption is available | Encryption is available | Work in progress - expected for the Mitaka release |
| Administrator configures size setting, based on flavors | Sizings based on need | Easily scalable for future growth |
| Example: 10 GB first disk, 30 GB/core second disk | Example: 1 TB "extra hard drive" | Example: 10s of TBs of data set storage |
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.