Openstack Cinder

The OpenStack platform is an open-source collaboration to develop a private cloud ecosystem, delivering IT services at web scale.

OpenStack is divided into a number of discrete projects, each with a code name with parallels to the purpose of the project itself like cinder , nova , neutron ,swift , horizon , shara etc

Virtual machines – or compute – are delivered through a project called Nova. In early OpenStack implementations, Nova virtual machines were stateless, that is they were not kept on persistent storage, and a Nova virtual machine would lose its contents when it was shut down.

As Nova developed, a feature called nova-volume was introduced to store virtual machines on persistent media, similar to the way Amazon Web Services Elastic Cloud Compute (EC2) stores instances on persistent media known as Elastic Block Store (EBS). The nova-volume feature was eventually superseded by a separate project called Cinder that delivers persistent block-level storage to OpenStack environments.How It works ?Cinder performs a number of operations in OpenStack environments. In the first instance it acts as a piece of middleware, providing application programming interfaces (APIs) that allow Cinder volumes to be created through use of the Cinder client software. A single/multiple Cinder volume(s) is associated with a single Nova compute instance or virtual machine. Cinder keeps track of the volumes in use within OpenStack using a MySQL database created on the Cinder services controller.DataBaseName : cinder
[root@openstack-lab ~]# mysql -u root -U cinderMariaDB [cinder]> show tables;
+----------------------------+| Tables_in_cinder |
+----------------------------+
| backups |
| cgsnapshots |
| consistencygroups |
| driver_initiator_data |
| encryption |
| image_volume_cache_entries |
| iscsi_targets |
| migrate_version |
| quality_of_service_specs |
| quota_classes |
| quota_usages |
| quotas |
| reservations |
| services |
| snapshot_metadata |
| snapshots |
| transfers |
| volume_admin_metadata |
| volume_attachment |
| volume_glance_metadata |
| volume_metadata |
| volume_type_extra_specs |
| volume_type_projects |
| volume_types |
| volumes |
+----------------------------+25 rows in set (0.00 sec)
MariaDB [cinder]>
Through the use of a common interface and APIs, Cinder abstracts the process of creating and attaching volumes to Nova compute instances. This means storage can be provided to OpenStack environments through a variety of methods.By default, Cinder volumes are created on a standard Linux server that runs Logical Volume Manager (LVM). This allows physical disks to be combined to implement redundant array of independent disks (RAID) data protection and to carve out logical volumes from a physical pool of space, called a volume group. Cinder volumes are created from a volume group called cinder-volumes, with the OpenStack administrator assigned the task of deciding exactly how this LVM group is mapped onto physical disk.There are multiple storage backend type which can be used to create cinder_volumes. 

# Storage backend to use for the Block Storage service; valid options are: [ lvm, gluster, nfs, vmdk, netapp. ['lvm', 'gluster', 'nfs', 'vmdk', 'netapp']

Cinder and external storage

Cinder can also manage external storage resources, either from a physical external storage array or from software-based storage implementations. This is achieved through the use of a Cinder driver that maps Cinder requests to the commands required on the external storage platform – in fact, the default LVM implementation is simply another Cinder driver. Support is available for iSCSI and Fibre Channel protocols, with specific support based on the capabilities of the supplier’s storage hardware (see the support matrix described later).

Some hardware platforms require storage administrators to create a pool – or pools – of storage for OpenStack to use – traditional arrays that use pools of RAID groups, for example.

A list of supported platforms is available but this isn’t exhaustive and many suppliers are not mentioned. You should check with your storage supplier for specific information on Cinder support and the features their drivers offer.

The use of external storage for OpenStack provides the ability to take advantage of native features on the storage platform where available, such as data deduplication, compression, thin provisioning and quality of service.

External storage isn’t limited to physical hardware appliances; block storage can be assigned to OpenStack from a variety of software-based systems, both commercial and open-source. This includes Ceph and GlusterFS. Ceph, for example, is implemented through the use of Rados Block Device (RBD), a device driver in the Linux kernel that talks natively with a Ceph storage cluster.

OpenStack Cinder features

With each successive release of OpenStack (the most recent being Mitaka – versions are named after successive letters of the alphabet), new features have been added to Cinder.