Once you have installed and configured your Ceph storage cluster, the next task is performing storage provisioning. Storage provisioning is the process of assigning storage space or capacity to physical or virtual servers, either in the form of block, file, or object storage. A typical computer system or server comes with a limited local storage capacity that might not be enough for your data storage needs.

Storage solutions such as Ceph provide virtually unlimited storage capacity to these servers, making them capable of storing all your data and making sure that you do not run out of space. Using a dedicated storage system instead of local storage gives you the much-needed flexibility in terms of scalability, reliability, and performance.

Ceph can provision storage capacity in a unified way, which includes block, filesystem, and object storage. The following diagram shows storage formats supported by Ceph, and depending on your use case, you can select one or more storage options:

We will discuss each of these options in detail in this book, but in this chapter, we will focus on Ceph block storage.

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 the 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:

Industry-leading open source hypervisors, such as KVM and Xen, provide full support to RBD and leverage its features on their guest virtual machines. Other proprietary hypervisors, such as VMware and Microsoft Hyper-V 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 OpenStack, CloudStack, 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.