.. _ceph_block_device:

=================== Ceph Block Device

.. index:: Ceph Block Device; introduction

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 :abbr:RADOS (Reliable Autonomic Distributed Object Store) capabilities including snapshotting, replication and strong consistency. Ceph block storage clients communicate with Ceph clusters through kernel modules or the librbd library.

.. ditaa::

        +------------------------+ +------------------------+
        |     Kernel Module      | |        librbd          |
        +------------------------+-+------------------------+
        |                   RADOS Protocol                  |
        +------------------------+-+------------------------+
        |          OSDs          | |        Monitors        |
        +------------------------+ +------------------------+

.. note:: 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 :abbr:KVMs (kernel virtual machines) 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 :ref:Ceph RADOS Gateway <object-gateway>, the :ref:Ceph File System <ceph-file-system>, and Ceph block devices simultaneously.

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

.. toctree:: :maxdepth: 1

Basic Commands <rados-rbd-cmds>

.. toctree:: :maxdepth: 2

    Operations <rbd-operations>

.. toctree:: :maxdepth: 2

    Integrations <rbd-integrations>

.. toctree:: :maxdepth: 2

Manpages <man/index>

.. toctree:: :maxdepth: 2

APIs <api/index>

.. _RBD Caching: ./rbd-config-ref/ .. _kernel modules: ./rbd-ko/ .. _QEMU: ./qemu-rbd/ .. _OpenStack: ./rbd-openstack .. _OpenNebula: https://docs.opennebula.io/stable/open_cluster_deployment/storage_setup/ceph_ds.html .. _CloudStack: ./rbd-cloudstack