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113 lines
3.5 KiB
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113 lines
3.5 KiB
ReStructuredText
====================
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RADOS RBD Commands
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====================
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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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Creating a Block Device Image
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-----------------------------
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Before you can add a block device to a Ceph client, you must create an image for
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it in the OSD cluster first. To create a block device image, execute the
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following::
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rbd create {image-name} --size {megabytes} --dest-pool {pool-name}
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For example, to create a 1GB image named ``foo`` that stores information in a
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pool named ``swimmingpool``, execute the following::
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rbd create foo --size 1024
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rbd create bar --size 1024 --pool swimmingpool
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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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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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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 --image {image-name} info
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For example::
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rbd --image foo info
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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 --image {image-name} -p {pool-name} info
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For example::
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rbd --image bar -p swimmingpool info
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Resizing a Block Device Image
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-----------------------------
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RBD images are thin provisioned. They don't actually use any physical storage
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until you begin saving data to them. However, they do have a maximum capacity
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that you set with the ``--size`` option. If you want to increase (or decrease)
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the maximum size of a RADOS block device image, execute the following::
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rbd resize --image foo --size 2048
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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 {image-name} -p {pool-name}
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For example::
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rbd rm bar -p swimmingpool
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Snapshotting Block Device Images
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--------------------------------
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One of the advanced features of RADOS block devices is that you can create
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snapshots of the images to retain a history of an image's state. Ceph supports
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RBD snapshots from the ``rbd`` command, from a kernel object, from a
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KVM, and from cloud solutions. Once you create snapshots of an image, you
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can rollback to a snapshot, list snapshots, remove snapshots and purge
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the snapshots.
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.. important:: Generally, you should stop i/o before snapshotting an image.
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If the image contains a filesystem, the filesystem should be in a
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consistent state before snapshotting too.
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.. _Storage Pools: ../../config-cluster/pools
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.. _RBD – Manage RADOS Block Device (RBD) Images: ../../man/8/rbd/ |