Cinder is the block storage service of OpenStack. Cinder is used to create and provide storage volumes. Once created, the volumes can be attached to an instance. Cinder takes care of all block storage management. Cinder is the equivalent of the Elastic Block Store (EBS) service of Amazon AWS. Using Cinder, a volume can only be attached to one instance at a time.

The block storage service contains the following components:

• Backend storage devices: Whenever a volume is created and provided to a user, the storage must come from a physical device. As such, there is a need for backend storage devices on which the services can be stored. By default, the LVM on a local volume group is used. These volumes are called Cinder volumes. In addition to this, Cinder also provides support for using other storage devices, such as external RAID arrays.
• Volumes: This is the equivalent of a hard disk. These volumes are persistent block storage devices. A volume is an allocated resource that can be attached to an instance. We have two types of volumes: volumes that store the OS image and volumes that are used to boot. These are known as root volumes. We can also have secondary volumes that are not root volumes. 
• Snapshots: These are point-in-time copies of a volume. Snapshots are read-only. A snapshot is created from a volume. Once a snapshot is created, we can recreate the volume from the snapshot. 
• Backups: These are archived copies of volumes. The backups are stored in the object storage service of OpenStack, called Swift.