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6.8 KiB
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224 lines
6.8 KiB
ReStructuredText
=======================
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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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#. On the admin node, use the ``ceph`` tool to `create a pool`_.
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#. On the admin node, use the ``rbd`` tool to initialize the pool for use by RBD::
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rbd pool init <pool-name>
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.. note:: The ``rbd`` tool assumes a default pool name of 'rbd' when not
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provided.
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Create a Block Device User
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==========================
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Unless specified, the ``rbd`` command will access the Ceph cluster using the ID
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``admin``. This ID allows full administrative access to the cluster. It is
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recommended that you utilize a more restricted user wherever possible.
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To `create a Ceph user`_, with ``ceph`` specify the ``auth get-or-create``
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command, user name, monitor caps, and OSD caps::
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ceph auth get-or-create client.{ID} mon 'profile rbd' osd 'profile {profile name} [pool={pool-name}][, profile ...]'
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For example, to create a user ID named ``qemu`` with read-write access to the
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pool ``vms`` and read-only access to the pool ``images``, execute the
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following::
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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'
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The output from the ``ceph auth get-or-create`` command will be the keyring for
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the specified user, which can be written to ``/etc/ceph/ceph.client.{ID}.keyring``.
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.. note:: The user ID can be specified when using the ``rbd`` command by
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providing the ``--id {id}`` optional argument.
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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` first. To create a block device image, execute
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the following::
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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``, execute the following::
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rbd create --size 1024 swimmingpool/bar
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If you don't specify pool when creating an image, it will be stored in the
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default pool ``rbd``. For example, to create a 1GB image named ``foo`` stored in
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the default pool ``rbd``, execute the following::
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rbd create --size 1024 foo
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.. note:: You must create a pool first before you can specify it as a
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source. See `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, execute the following
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(i.e., ``rbd`` is the default pool name)::
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rbd ls
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To list block devices in a particular pool, execute the following,
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but replace ``{poolname}`` with the name of the pool::
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rbd ls {poolname}
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For example::
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rbd ls swimmingpool
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To list deferred delete block devices in the ``rbd`` pool, execute the
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following::
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rbd trash ls
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To list deferred delete block devices in a particular pool, execute the
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following, but replace ``{poolname}`` with the name of the pool::
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rbd trash ls {poolname}
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For example::
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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, execute the following,
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but replace ``{image-name}`` with the name for the image::
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rbd info {image-name}
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For example::
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rbd info foo
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To retrieve information from an image within a pool, execute the following,
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but replace ``{image-name}`` with the name of the image and replace ``{pool-name}``
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with the name of the pool::
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rbd info {pool-name}/{image-name}
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For example::
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rbd info swimmingpool/bar
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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, execute
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the following::
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rbd resize --size 2048 foo (to increase)
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rbd resize --size 2048 foo --allow-shrink (to decrease)
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Removing a Block Device Image
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=============================
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To remove a block device, execute the following, but replace ``{image-name}``
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with the name of the image you want to remove::
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rbd rm {image-name}
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For example::
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rbd rm foo
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To remove a block device from a pool, execute the following, but replace
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``{image-name}`` with the name of the image to remove and replace
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``{pool-name}`` with the name of the pool::
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rbd rm {pool-name}/{image-name}
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For example::
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rbd rm swimmingpool/bar
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To defer delete a block device from a pool, execute the following, but
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replace ``{image-name}`` with the name of the image to move and replace
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``{pool-name}`` with the name of the pool::
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rbd trash mv {pool-name}/{image-name}
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For example::
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rbd trash mv swimmingpool/bar
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To remove a deferred block device from a pool, execute the following, but
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replace ``{image-id}`` with the id of the image to remove and replace
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``{pool-name}`` with the name of the pool::
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rbd trash rm {pool-name}/{image-id}
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For example::
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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 it has shapshot(s) or actively
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in-use by clones, but can not be removed from trash.
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* You can use *--delay* to set the defer time (default is 0), and if its
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deferment time has not expired, it can not be removed unless you use
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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, execute the
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following, but replace ``{image-id}`` with the id of the image::
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rbd trash restore {image-d}
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For example::
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rbd trash restore 2bf4474b0dc51
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To restore a deferred delete block device in a particular pool, execute
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the following, 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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rbd trash restore {pool-name}/{image-id}
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For example::
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rbd trash restore swimmingpool/2bf4474b0dc51
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Also you can use *--image* to rename the iamge when restore it, for
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example::
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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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