Block Device Commands

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 Ceph Storage Cluster first. To create a block device image, execute the following:

rbd create {image-name} --size {megabytes} --pool {pool-name}

For example, to create a 1GB image named bar that stores information in a pool named swimmingpool, execute the following:

rbd create bar --size 1024 --pool swimmingpool

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 foo --size 1024

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 --image {image-name} info

For example:

rbd --image foo info

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 --image {image-name} -p {pool-name} info

For example:

rbd --image bar -p swimmingpool info

Resizing a Block Device Image

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 --image foo --size 2048

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 {image-name} -p {pool-name}

For example:

rbd rm bar -p swimmingpool