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327 lines
8.8 KiB
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327 lines
8.8 KiB
ReStructuredText
=============================
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Basic Block Device Commands
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=============================
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.. index:: Ceph Block Device; image management
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The ``rbd`` command enables you to create, list, introspect and remove block
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device images. You can also use it to clone images, create snapshots,
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rollback an image to a snapshot, view a snapshot, etc. For details on using
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the ``rbd`` command, see `RBD – Manage RADOS Block Device (RBD) Images`_ for
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details.
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.. important:: To use Ceph Block Device commands, you must have access to
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a running Ceph cluster.
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Create a Block Device Pool
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==========================
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#. Use the ``ceph`` tool to `create a pool`_.
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#. Use the ``rbd`` tool to initialize the pool for use by RBD:
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.. prompt:: bash $
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rbd pool init <pool-name>
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.. note:: The ``rbd`` tool assumes a default pool name of 'rbd' if no pool
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name is specified in the command.
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Create a Block Device User
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==========================
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Unless otherwise specified, the ``rbd`` command uses the Ceph user ID ``admin``
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to access the Ceph cluster. The ``admin`` Ceph user ID allows full
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administrative access to the cluster. We recommend that you acess the Ceph
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cluster with a Ceph user ID that has fewer permissions than the ``admin`` Ceph
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user ID does. We call this non-``admin`` Ceph user ID a "block device user" or
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"Ceph user".
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To `create a Ceph user`_, use the ``ceph auth get-or-create`` command to
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specify the Ceph user ID name, monitor caps (capabilities), and OSD caps
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(capabilities):
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.. prompt:: bash $
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ceph auth get-or-create client.{ID} mon 'profile rbd' osd 'profile {profile name} [pool={pool-name}][, profile ...]' mgr 'profile rbd [pool={pool-name}]'
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For example: to create a Ceph user ID named ``qemu`` that has read-write access
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to the pool ``vms`` and read-only access to the pool ``images``, run the
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following command:
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.. prompt:: bash $
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ceph auth get-or-create client.qemu mon 'profile rbd' osd 'profile rbd pool=vms, profile rbd-read-only pool=images' mgr 'profile rbd pool=images'
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The output from the ``ceph auth get-or-create`` command is the keyring for the
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specified Ceph user ID, which can be written to
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``/etc/ceph/ceph.client.{ID}.keyring``.
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.. note:: Specify the Ceph user ID by providing the ``--id {id} argument when
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using the ``rbd`` command. This argument is optional.
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Creating a Block Device Image
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=============================
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Before you can add a block device to a node, you must create an image for it in
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the :term:`Ceph Storage Cluster`. To create a block device image, run a command of this form:
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.. prompt:: bash $
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rbd create --size {megabytes} {pool-name}/{image-name}
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For example, to create a 1GB image named ``bar`` that stores information in a
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pool named ``swimmingpool``, run this command:
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.. prompt:: bash $
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rbd create --size 1024 swimmingpool/bar
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If you don't specify a pool when you create an image, then the image will be
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stored in the default pool ``rbd``. For example, if you ran this command, you
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would create a 1GB image named ``foo`` that is stored in the default pool
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``rbd``:
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.. prompt:: bash $
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rbd create --size 1024 foo
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.. note:: You must create a pool before you can specify it as a source. See
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`Storage Pools`_ for details.
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Listing Block Device Images
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===========================
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To list block devices in the ``rbd`` pool, run the following command:
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.. prompt:: bash $
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rbd ls
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.. note:: ``rbd`` is the default pool name, and ``rbd ls`` lists the commands
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in the default pool.
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To list block devices in a particular pool, run the following command, but
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replace ``{poolname}`` with the name of the pool:
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.. prompt:: bash $
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rbd ls {poolname}
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For example:
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.. prompt:: bash $
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rbd ls swimmingpool
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To list "deferred delete" block devices in the ``rbd`` pool, run the
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following command:
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.. prompt:: bash $
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rbd trash ls
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To list "deferred delete" block devices in a particular pool, run the
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following command, but replace ``{poolname}`` with the name of the pool:
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.. prompt:: bash $
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rbd trash ls {poolname}
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For example:
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.. prompt:: bash $
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rbd trash ls swimmingpool
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Retrieving Image Information
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============================
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To retrieve information from a particular image, run the following command, but
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replace ``{image-name}`` with the name for the image:
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.. prompt:: bash $
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rbd info {image-name}
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For example:
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.. prompt:: bash $
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rbd info foo
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To retrieve information from an image within a pool, run the following command,
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but replace ``{image-name}`` with the name of the image and replace
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``{pool-name}`` with the name of the pool:
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.. prompt:: bash $
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rbd info {pool-name}/{image-name}
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For example:
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.. prompt:: bash $
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rbd info swimmingpool/bar
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.. note:: Other naming conventions are possible, and might conflict with the
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naming convention described here. For example, ``userid/<uuid>`` is a
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possible name for an RBD image, and such a name might (at the least) be
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confusing.
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Resizing a Block Device Image
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=============================
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:term:`Ceph Block Device` images are thin provisioned. They don't actually use
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any physical storage until you begin saving data to them. However, they do have
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a maximum capacity that you set with the ``--size`` option. If you want to
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increase (or decrease) the maximum size of a Ceph Block Device image, run one
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of the following commands:
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Increasing the Size of a Block Device Image
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-------------------------------------------
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.. prompt:: bash $
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rbd resize --size 2048 foo
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Decreasing the Size of a Block Device Image
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-------------------------------------------
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.. prompt:: bash $
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rbd resize --size 2048 foo --allow-shrink
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Removing a Block Device Image
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=============================
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To remove a block device, run the following command, but replace
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``{image-name}`` with the name of the image you want to remove:
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.. prompt:: bash $
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rbd rm {image-name}
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For example:
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.. prompt:: bash $
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rbd rm foo
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Removing a Block Device from a Pool
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-----------------------------------
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To remove a block device from a pool, run the following command but replace
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``{image-name}`` with the name of the image to be removed, and replace
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``{pool-name}`` with the name of the pool from which the image is to be
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removed:
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.. prompt:: bash $
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rbd rm {pool-name}/{image-name}
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For example:
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.. prompt:: bash $
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rbd rm swimmingpool/bar
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"Defer Deleting" a Block Device from a Pool
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-------------------------------------------
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To defer delete a block device from a pool (which entails moving it to the
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"trash" and deleting it later), run the following command but replace
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``{image-name}`` with the name of the image to be moved to the trash and
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replace ``{pool-name}`` with the name of the pool:
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.. prompt:: bash $
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rbd trash mv {pool-name}/{image-name}
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For example:
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.. prompt:: bash $
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rbd trash mv swimmingpool/bar
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Removing a Deferred Block Device from a Pool
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--------------------------------------------
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To remove a deferred block device from a pool, run the following command but
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replace ``{image-}`` with the ID of the image to be removed, and replace
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``{pool-name}`` with the name of the pool from which the image is to be
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removed:
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.. prompt:: bash $
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rbd trash rm {pool-name}/{image-}
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For example:
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.. prompt:: bash $
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rbd trash rm swimmingpool/2bf4474b0dc51
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.. note::
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* You can move an image to the trash even if it has snapshot(s) or is
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actively in use by clones. However, you cannot remove it from the trash
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under those conditions.
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* You can use ``--expires-at`` to set the deferment time (default is
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``now``). If the deferment time has not yet arrived, you cannot remove the
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image unless you use ``--force``.
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Restoring a Block Device Image
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==============================
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To restore a deferred delete block device in the rbd pool, run the
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following command but replace ``{image-id}`` with the ID of the image:
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.. prompt:: bash $
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rbd trash restore {image-id}
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For example:
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.. prompt:: bash $
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rbd trash restore 2bf4474b0dc51
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Restoring a Block Device Image in a Specific Pool
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-------------------------------------------------
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To restore a deferred delete block device in a particular pool, run the
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following command but replace ``{image-id}`` with the ID of the image and
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replace ``{pool-name}`` with the name of the pool:
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.. prompt:: bash $
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rbd trash restore {pool-name}/{image-id}
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For example:
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.. prompt:: bash $
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rbd trash restore swimmingpool/2bf4474b0dc51
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Renaming an Image While Restoring It
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------------------------------------
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You can also use ``--image`` to rename the image while restoring it.
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For example:
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.. prompt:: bash $
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rbd trash restore swimmingpool/2bf4474b0dc51 --image new-name
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.. _create a pool: ../../rados/operations/pools/#create-a-pool
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.. _Storage Pools: ../../rados/operations/pools
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.. _RBD – Manage RADOS Block Device (RBD) Images: ../../man/8/rbd/
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.. _create a Ceph user: ../../rados/operations/user-management#add-a-user
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