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===============
Block Devices
===============
A block is a sequence of bytes (for example, a 512-byte block of data).
Block-based storage interfaces are the most common way to store data with
rotating media such as hard disks, CDs, floppy disks, and even traditional
9-track tape. The ubiquity of block device interfaces makes a virtual block
device an ideal candidate to interact with a mass data storage system like Ceph.
Ceph's RADOS Block Devices (RBD) interact with RADOS OSDs using the
``librados`` and ``librbd`` libraries. RBDs are thin-provisioned, resizable
and store data striped over multiple OSDs in a Ceph cluster. RBDs inherit
``librados`` capabilities such as snapshotting and cloning. Ceph's RBDs deliver
high performance with infinite scalability to kernel objects, kernel virtual
machines and cloud-based computing systems like OpenStack and CloudStack.
The ``librbd`` library converts data blocks into objects for storage in
RADOS OSD clusters--the same storage system for ``librados`` object stores and
the Ceph FS filesystem. You can use the same cluster to operate object stores,
the Ceph FS filesystem, and RADOS block devices simultaneously.
.. toctree::
:maxdepth: 1
RADOS Commands <rados-rbd-cmds>
Kernel Objects <rbd-ko>
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