This document is for a development version of Ceph.

Ceph Block Device

A block is a sequence of bytes (often 512). Block-based storage interfaces are a mature and common way to store data on media including HDDs, SSDs, CDs, floppy disks, and even tape. The ubiquity of block device interfaces is a perfect fit for interacting with mass data storage including Ceph.

Ceph block devices are thin-provisioned, resizable, and store data striped over multiple OSDs. Ceph block devices leverage RADOS capabilities including snapshotting, replication and strong consistency. Ceph block storage clients communicate with Ceph clusters through kernel modules or the librbd library.


Kernel modules can use Linux page caching. For librbd-based applications, Ceph supports RBD Caching.

Ceph’s block devices deliver high performance with vast scalability to kernel modules, or to KVMs such as QEMU, and cloud-based computing systems like OpenStack, OpenNebula and CloudStack that rely on libvirt and QEMU to integrate with Ceph block devices. You can use the same cluster to operate the Ceph RADOS Gateway, the Ceph File System, and Ceph block devices simultaneously.


To use Ceph Block Devices, you must have access to a running Ceph cluster.

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