Chapter 1. Introduction to Ceph block devices

A block is a set length of bytes in a sequence, for example, a 512-byte block of data. Combining many blocks together into a single file can be used as a storage device that you can read from and write to. Block-based storage interfaces are the most common way to store data with rotating media such as:

  • Hard drives
  • CD/DVD discs
  • Floppy disks
  • Traditional 9-track tapes

The ubiquity of block device interfaces makes a virtual block device an ideal candidate for interacting with a mass data storage system like Red Hat Ceph Storage.

Ceph block devices are thin-provisioned, resizable and store data striped over multiple Object Storage Devices (OSD) in a Ceph storage cluster. Ceph block devices are also known as Reliable Autonomic Distributed Object Store (RADOS) Block Devices (RBDs). Ceph block devices leverage RADOS capabilities such as:

  • Snapshots
  • Replication
  • Data consistency

Ceph block devices interact with OSDs by using the librbd library.

Ceph block devices deliver high performance with infinite scalability to Kernel Virtual Machines (KVMs), such as Quick Emulator (QEMU), and cloud-based computing systems, like OpenStack, that rely on the libvirt and QEMU utilities to integrate with Ceph block devices. You can use the same storage cluster to operate the Ceph Object Gateway and Ceph block devices simultaneously.


To use Ceph block devices, requires you to have access to a running Ceph storage cluster. For details on installing a Red Hat Ceph Storage cluster, see the Red Hat Ceph Storage Installation Guide.