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ceph/doc/rbd/rados-rbd-cmds.rst
Yehua 777564c870 doc:adding "--allow-shrink" in decreasing the size of the rbd block to distinguish from the increasing option
In the original file, the increasing and decreaing of the size of the rbd block shares the same option:
    "rbd resize --size 2048 foo".
However, it is not proper, as the "--allow-shrink" needs to be added while decreasing the size of the rbd block.
As a result, it is necessary to make a distinguish between these two options as follows:
    "rbd resize --size 2048 foo (to increase)"
    "rbd resize --size 2048 foo --allow-shrink (to decrease)"

Signed-off-by: Yehua <chen.yehua@h3c.com>
2015-12-23 13:13:04 +08:00

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=======================
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/