OpenStack Cinder is responsible for handling block storage in the context of OpenStack. Cinder provides a standard API and interface that allows storage companies to create their own drivers in order to integrate storage capabilities into OpenStack in a consistent way. Each storage pool exposed to OpenStack Cinder is a backend and you can have many storage backends. You can also have many of the same kind of storage backends. In this article we will look at two advanced features Cinder provides: types and the scheduler.
Cinder types essentially allow us to label Cinder storage backends. This allows for building out storage services that have expected characteristics and capabilities. The Cinder driver exposes those storage capabilities to Cinder.
The Cinder scheduler is responsible for deciding where to create Cinder volumes when we have more than one of the same kind of storage backend. This is done by looking at the filter rules in order to identify the most appropriate storage backend. More about filter rules can be found here.