The Ceph Block Device, formerly known as RADOS Block Device, provides reliable, distributed, and high performance block storage disks to clients. A RADOS block device makes use of the librbd library and stores a block of data in sequential form striped over multiple OSDs in a Ceph cluster. RBD is backed by the RADOS layer of Ceph, thus every block device is spread over multiple Ceph nodes, delivering high performance and excellent reliability. RBD has native support for Linux kernel, which means that RBD drivers are well integrated with the Linux kernel since past few years. In addition to reliability and performance, RBD also provides enterprise features such as full and incremental snapshots, thin provisioning, copy on write cloning, dynamic resizing, and so on. RBD also supports In-Memory caching, which drastically improves its performance.

The industry leading open source hypervisors, such as KVM and Zen, provide full support to RBD and leverage its features on their guest virtual machines. Other proprietary hypervisors, such as VMware and Microsoft HyperV will be supported very soon. There has been a lot of work going on in the community to support these hypervisors. The Ceph block device provides full support to cloud platforms such as Open Stack, Cloud Stack, as well as others. It has been proven successful and feature-rich for these cloud platforms. In OpenStack, you can use the Ceph block device with cinder (block) and glance (imaging) components. Doing so, you can spin thousands of Virtual Machines (VMs) in very little time, taking advantage of the copy on write feature of the Ceph block storage.

All these features make RBD an ideal candidate for cloud platforms such as OpenStack and CloudStack. We will now learn how to create a Ceph block device and make use of it.