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Chapter 9. Using the Ceph block device Python module
The rbd
python module provides file-like access to Ceph block device images. In order to use this built-in tool, import the rbd
and rados
Python modules.
Prerequisites
- A running Red Hat Ceph Storage cluster.
- Root-level access to the node.
Procedure
Connect to RADOS and open an IO context:
cluster = rados.Rados(conffile='my_ceph.conf') cluster.connect() ioctx = cluster.open_ioctx('mypool')
Instantiate an
:class:rbd.RBD
object, which you use to create the image:rbd_inst = rbd.RBD() size = 4 * 1024**3 # 4 GiB rbd_inst.create(ioctx, 'myimage', size)
To perform I/O on the image, instantiate an
:class:rbd.Image
object:image = rbd.Image(ioctx, 'myimage') data = 'foo' * 200 image.write(data, 0)
This writes 'foo' to the first 600 bytes of the image. Note that data cannot be
:type:unicode
-librbd
does not know how to deal with characters wider than a:c:type:char
.Close the image, the IO context and the connection to RADOS:
image.close() ioctx.close() cluster.shutdown()
To be safe, each of these calls must to be in a separate
:finally
block:import rados import rbd cluster = rados.Rados(conffile='my_ceph_conf') try: ioctx = cluster.open_ioctx('my_pool') try: rbd_inst = rbd.RBD() size = 4 * 1024**3 # 4 GiB rbd_inst.create(ioctx, 'myimage', size) image = rbd.Image(ioctx, 'myimage') try: data = 'foo' * 200 image.write(data, 0) finally: image.close() finally: ioctx.close() finally: cluster.shutdown()
This can be cumbersome, so the Rados, Ioctx, and Image classes can be used as context managers that close or shut down automatically. Using them as context managers, the above example becomes:
with rados.Rados(conffile='my_ceph.conf') as cluster: with cluster.open_ioctx('mypool') as ioctx: rbd_inst = rbd.RBD() size = 4 * 1024**3 # 4 GiB rbd_inst.create(ioctx, 'myimage', size) with rbd.Image(ioctx, 'myimage') as image: data = 'foo' * 200 image.write(data, 0)