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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