=======================
 Block Device Commands
=======================

.. index:: Ceph Block Device; image management

The ``rbd`` command enables you to create, list, introspect and remove block
device images. You can also use it to clone images, create snapshots,
rollback an image to a snapshot, view a snapshot, etc. For details on using
the ``rbd`` command, see `RBD – Manage RADOS Block Device (RBD) Images`_ for
details. 

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


Creating a Block Device Image
=============================

Before you can add a block device to a node, you must create an image for it in
the :term:`Ceph Storage Cluster` first. To create a block device image, execute
the  following::

	rbd create --size {megabytes} {pool-name}/{image-name}
	
For example, to create a 1GB image named ``bar`` that stores information in a
pool named ``swimmingpool``, execute the following::

	rbd create --size 1024 swimmingpool/bar

If you don't specify pool when creating an image, it will be stored in the
default pool ``rbd``. For example, to create a 1GB image named ``foo`` stored in
the default pool ``rbd``, execute the following::

	rbd create --size 1024 foo

.. note:: You must create a pool first before you can specify it as a 
   source. See `Storage Pools`_ for details.

Listing Block Device Images
===========================

To list block devices in the ``rbd`` pool, execute the following
(i.e., ``rbd`` is the default pool name):: 

	rbd ls

To list block devices in a particular pool, execute the following,
but replace ``{poolname}`` with the name of the pool:: 

	rbd ls {poolname}
	
For example::

	rbd ls swimmingpool
	
Retrieving Image Information
============================

To retrieve information from a particular image, execute the following,
but replace ``{image-name}`` with the name for the image:: 

	rbd info {image-name}
	
For example::

	rbd info foo
	
To retrieve information from an image within a pool, execute the following,
but replace ``{image-name}`` with the name of the image and replace ``{pool-name}``
with the name of the pool:: 

	rbd info {pool-name}/{image-name}

For example:: 

	rbd info swimmingpool/bar

Resizing a Block Device Image
=============================

:term:`Ceph Block Device` images are thin provisioned. They don't actually use
any physical storage  until you begin saving data to them. However, they do have
a maximum capacity  that you set with the ``--size`` option. If you want to
increase (or decrease) the maximum size of a Ceph Block Device image, execute
the following:: 

	rbd resize --size 2048 foo (to increase)
	rbd resize --size 2048 foo --allow-shrink (to decrease)


Removing a Block Device Image
=============================

To remove a block device, execute the following, but replace ``{image-name}``
with the name of the image you want to remove:: 

	rbd rm {image-name}
	
For example:: 

	rbd rm foo
	
To remove a block device from a pool, execute the following, but replace 
``{image-name}`` with the name of the image to remove and replace 
``{pool-name}`` with the name of the pool:: 

	rbd rm {pool-name}/{image-name}
	
For example:: 

	rbd rm swimmingpool/bar



.. _Storage Pools: ../../rados/operations/pools
.. _RBD – Manage RADOS Block Device (RBD) Images: ../../man/8/rbd/