The OpenStack Block Storage Service is code named Cinder. It provides persistent block storage volumes that can be attached to virtual machines running on OpenStack. This service is slightly similar to Amazon EBS where a volume can be carved out of the underlying disk and attached to the instance. It should be noted that one volume can be attached to only one virtual machine instance.

The OpenStack Block Storage Service has the following components:

• cinder-api: This provides a WSGI interface that authenticates and routes the requests to the Cinder service
• cinder-scheduler: This component schedules and routes requests to the appropriate volume service based certain parameters 
• cinder-volume: This component manages block storage devices
• cinder-backup: Provides a backup and restore mechanism for the block storage to OpenStack Swift
• cinder-db: Cinder stores all volume information in the Cinder database

The following diagram indicates the interaction of Cinder services:

The cinder-volume service can interact with several hardware providers such as Dell EMC, IBM, and so on by enabling the appropriate driver in the Cinder configuration. By default, Cinder uses the LVM driver.

The following screenshot shows the OpenStack Cinder user interface. It shows that a  single disk volume is created and is in the In-use state. Note the Type column shows the driver as lvmdriver-1 which indicates that the LVM driver is used to create the volume. In other words, when a Cinder volume is created, an LVM volume gets created underneath on the Cinder node: