To use the Block Storage API effectively, you must understand several key concepts:
Volume
A detachable block storage device. You can think of it as a USB hard drive. It can only be attached to one instance at a time.
Volume type
A type of a block storage volume. You can define whatever types work best for you, such as SATA, SCSCI, SSD, etc. These can be customized or defined by the OpenStack admin.
You can also define extra_specs associated with your volume types. For instance, you could have a VolumeType=SATA, with extra_specs (RPM=10000, RAID-Level=5) . Extra_specs are defined and customized by the admin.
Snapshot
A point in time copy of the data contained in a volume.
Instance
A virtual machine (VM) that runs inside the cloud.
Backup
A full copy of a volume stored in an external service. The service can be configured. The only supported service for now is Object Storage. A backup can subsequently be restored from the external service to either the same volume that the backup was originally taken from, or to a new volume.
