===================
 RBD and OpenStack
===================

You may use Ceph block device images with OpenStack with QEMU and ``libvirt`` as
the interface. Ceph stripes block device images as objects across the  cluster,
which means that large Ceph block device images have better  performance than a
standalone server!

To use RBD with OpenStack, you must install QEMU, ``libvirt``, and OpenStack
first. We recommend using a separate physical host for your OpenStack
installation. OpenStack recommends a minimum of  8GB of RAM and a quad-core
processor. The following diagram depicts the OpenStack/Ceph technology stack.


.. ditaa::  +---------------------------------------------------+
            |                    OpenStack                      |
            +---------------------------------------------------+            
            |                     libvirt                       |
            +---------------------------------------------------+            
            |                     QEMU/RBD                      |
            +---------------------------------------------------+
            |                      librbd                       |
            +---------------------------------------------------+
            |                     librados                      |
            +------------------------+-+------------------------+
            |          OSDs          | |        Monitors        |
            +------------------------+ +------------------------+

.. _Installing OpenStack: ../../install/openstack

.. important:: To use RBD with OpenStack, you must have a running Ceph cluster.


Create a Pool
=============

By default, RBD uses the ``data`` pool. You may use any available RBD pool. 
We recommend creating a pool for Nova. Ensure your Ceph cluster is running, 
then create a pool. ::

	ceph osd pool create nova

See `Create a Pool`_ for detail on specifying the number of placement groups
for your pool, and `Placement Groups`_ for details on the number of placement
groups you should set for your pool. 

.. _Create a Pool: ../../cluster-ops/pools#createpool
.. _Placement Groups: ../../cluster-ops/placement-groups

Install Ceph Common on the OpenStack Host
=========================================

OpenStack operates as a Ceph client. You must install Ceph common on the 
OpenStack host, and copy your Ceph cluster's ``ceph.conf`` file to the 
``/etc/ceph`` directory. If you have installed Ceph on the host, ceph-common
is already included. :: 

	sudo apt-get install ceph-common
	cd /etc/ceph
	ssh your-openstack-server sudo tee /etc/ceph/ceph.conf <ceph.conf


Add the RBD Driver and the Pool Name to ``nova.conf``
=====================================================

OpenStack requires a driver to interact with RADOS block devices. You must also
specify the pool name for the block device. On your OpenStack host, navigate to
the ``/etc/nova`` directory. Open the ``nova.conf`` file in a text editor using
sudo privileges and add the following lines to the file::

	volume_driver=nova.volume.driver.RBDDriver
	rbd_pool=nova


Restart OpenStack
=================

To activate the RBD driver and load the RBD pool name into the configuration,
you must restart OpenStack. Navigate the directory where you installed 
OpenStack, and execute the following:: 

	./rejoin-stack.sh

If you have OpenStack configured as a service, you can also execute:: 

	sudo service nova-volume restart

Once OpenStack is up and running, you should be able to create a volume with 
OpenStack on a Ceph RADOS block device.