Ceph Block Device python module

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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

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A running IBM Storage Ceph cluster.
Root-level access to the node.

Procedure

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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)