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===================
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`_ 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
.. _CloudStack: ./rbd-cloudstack
|
