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=============================
Block Devices and OpenStack
=============================
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.. index :: Ceph Block Device; OpenStack
You may use Ceph Block Device images with OpenStack through `` libvirt `` , which
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configures the QEMU interface to `` librbd `` . Ceph stripes block device images as
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objects across the cluster, which means that large Ceph Block Device images have
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better performance than a standalone server!
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To use Ceph Block Devices with OpenStack, you must install QEMU, `` libvirt `` ,
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and OpenStack first. We recommend using a separate physical node for your
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OpenStack installation. OpenStack recommends a minimum of 8GB of RAM and a
quad-core processor. The following diagram depicts the OpenStack/Ceph
technology stack.
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.. ditaa :: +---------------------------------------------------+
| OpenStack |
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+---------------------------------------------------+
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| libvirt |
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+------------------------+--------------------------+
|
| configures
v
+---------------------------------------------------+
| QEMU |
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+---------------------------------------------------+
| librbd |
+---------------------------------------------------+
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| librados |
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+------------------------+-+------------------------+
| OSDs | | Monitors |
+------------------------+ +------------------------+
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.. important :: To use Ceph Block Devices with OpenStack, you must have
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access to a running Ceph Storage Cluster.
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Three parts of OpenStack integrate with Ceph's block devices:
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- **Images** : OpenStack Glance manages images for VMs. Images are immutable.
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OpenStack treats images as binary blobs and downloads them accordingly.
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- **Volumes** : Volumes are block devices. OpenStack uses volumes to boot VMs,
or to attach volumes to running VMs. OpenStack manages volumes using
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Cinder services.
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- **Guest Disks** : Guest disks are guest operating system disks. By default,
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when you boot a virtual machine, its disk appears as a file on the filesystem
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of the hypervisor (usually under `` /var/lib/nova/instances/<uuid>/ `` ). Prior
to OpenStack Havana, the only way to boot a VM in Ceph was to use the
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boot-from-volume functionality of Cinder. However, now it is possible to boot
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every virtual machine inside Ceph directly without using Cinder, which is
advantageous because it allows you to perform maintenance operations easily
with the live-migration process. Additionally, if your hypervisor dies it is
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also convenient to trigger `` nova evacuate `` and run the virtual machine
elsewhere almost seamlessly.
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You can use OpenStack Glance to store images in a Ceph Block Device, and you
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can use Cinder to boot a VM using a copy-on-write clone of an image.
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The instructions below detail the setup for Glance, Cinder and Nova, although
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they do not have to be used together. You may store images in Ceph block devices
while running VMs using a local disk, or vice versa.
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.. important :: Using QCOW2 for hosting a virtual machine disk is NOT recommended.
If you want to boot virtual machines in Ceph (ephemeral backend or boot
from volume), please use the `` raw `` image format within Glance.
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.. index :: pools; OpenStack
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Create a Pool
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=============
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By default, Ceph block devices use the `` rbd `` pool. You may use any available
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pool. We recommend creating a pool for Cinder and a pool for Glance. Ensure
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your Ceph cluster is running, then create the pools. ::
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ceph osd pool create volumes 128
ceph osd pool create images 128
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ceph osd pool create backups 128
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ceph osd pool create vms 128
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See `Create a Pool`_ for detail on specifying the number of placement groups for
your pools, and `Placement Groups`_ for details on the number of placement
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groups you should set for your pools.
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Newly created pools must initialized prior to use. Use the `` rbd `` tool
to initialize the pools::
rbd pool init volumes
rbd pool init images
rbd pool init backups
rbd pool init vms
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.. _Create a Pool: ../../rados/operations/pools#createpool
.. _Placement Groups: ../../rados/operations/placement-groups
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Configure OpenStack Ceph Clients
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================================
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The nodes running `` glance-api `` , `` cinder-volume `` , `` nova-compute `` and
`` cinder-backup `` act as Ceph clients. Each requires the `` ceph.conf `` file::
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ssh {your-openstack-server} sudo tee /etc/ceph/ceph.conf </etc/ceph/ceph.conf
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Install Ceph client packages
----------------------------
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On the `` glance-api `` node, you will need the Python bindings for `` librbd `` ::
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sudo apt-get install python-rbd
sudo yum install python-rbd
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On the `` nova-compute `` , `` cinder-backup `` and on the `` cinder-volume `` node,
use both the Python bindings and the client command line tools::
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sudo apt-get install ceph-common
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sudo yum install ceph-common
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Setup Ceph Client Authentication
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--------------------------------
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If you have `cephx authentication`_ enabled, create a new user for Nova/Cinder
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and Glance. Execute the following::
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ceph auth get-or-create client.glance mon 'profile rbd' osd 'profile rbd pool=images'
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ceph auth get-or-create client.cinder mon 'profile rbd' osd 'profile rbd pool=volumes, profile rbd pool=vms, profile rbd-read-only pool=images'
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ceph auth get-or-create client.cinder-backup mon 'profile rbd' osd 'profile rbd pool=backups'
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Add the keyrings for `` client.cinder `` , `` client.glance `` , and
`` client.cinder-backup `` to the appropriate nodes and change their ownership::
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ceph auth get-or-create client.glance | ssh {your-glance-api-server} sudo tee /etc/ceph/ceph.client.glance.keyring
ssh {your-glance-api-server} sudo chown glance:glance /etc/ceph/ceph.client.glance.keyring
ceph auth get-or-create client.cinder | ssh {your-volume-server} sudo tee /etc/ceph/ceph.client.cinder.keyring
ssh {your-cinder-volume-server} sudo chown cinder:cinder /etc/ceph/ceph.client.cinder.keyring
ceph auth get-or-create client.cinder-backup | ssh {your-cinder-backup-server} sudo tee /etc/ceph/ceph.client.cinder-backup.keyring
ssh {your-cinder-backup-server} sudo chown cinder:cinder /etc/ceph/ceph.client.cinder-backup.keyring
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Nodes running `` nova-compute `` need the keyring file for the `` nova-compute ``
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process::
ceph auth get-or-create client.cinder | ssh {your-nova-compute-server} sudo tee /etc/ceph/ceph.client.cinder.keyring
They also need to store the secret key of the `` client.cinder `` user in
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`` libvirt `` . The libvirt process needs it to access the cluster while attaching
a block device from Cinder.
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Create a temporary copy of the secret key on the nodes running
`` nova-compute `` ::
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ceph auth get-key client.cinder | ssh {your-compute-node} tee client.cinder.key
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Then, on the compute nodes, add the secret key to `` libvirt `` and remove the
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temporary copy of the key::
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uuidgen
457eb676-33da-42ec-9a8c-9293d545c337
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cat > secret.xml <<EOF
<secret ephemeral='no' private='no'>
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<uuid>457eb676-33da-42ec-9a8c-9293d545c337</uuid>
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<usage type='ceph'>
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<name>client.cinder secret</name>
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</usage>
</secret>
EOF
sudo virsh secret-define --file secret.xml
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Secret 457eb676-33da-42ec-9a8c-9293d545c337 created
sudo virsh secret-set-value --secret 457eb676-33da-42ec-9a8c-9293d545c337 --base64 $(cat client.cinder.key) && rm client.cinder.key secret.xml
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Save the uuid of the secret for configuring `` nova-compute `` later.
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.. important :: You don't necessarily need the UUID on all the compute nodes.
However from a platform consistency perspective, it's better to keep the
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same UUID.
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.. _cephx authentication: ../../rados/configuration/auth-config-ref/#enabling-disabling-cephx
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Configure OpenStack to use Ceph
===============================
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Configuring Glance
------------------
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Glance can use multiple back ends to store images. To use Ceph block devices by
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default, configure Glance like the following.
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Kilo and after
~~~~~~~~~~~~~~
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Edit `` /etc/glance/glance-api.conf `` and add under the `` [glance_store] `` section::
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[glance_store]
stores = rbd
default_store = rbd
rbd_store_pool = images
rbd_store_user = glance
rbd_store_ceph_conf = /etc/ceph/ceph.conf
rbd_store_chunk_size = 8
For more information about the configuration options available in Glance please refer to the OpenStack Configuration Reference: http://docs.openstack.org/.
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Enable copy-on-write cloning of images
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Note that this exposes the back end location via Glance's API, so the endpoint
with this option enabled should not be publicly accessible.
Any OpenStack version except Mitaka
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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If you want to enable copy-on-write cloning of images, also add under the `` [DEFAULT] `` section::
show_image_direct_url = True
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Disable cache management (any OpenStack version)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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Disable the Glance cache management to avoid images getting cached under `` /var/lib/glance/image-cache/ `` ,
assuming your configuration file has `` flavor = keystone+cachemanagement `` ::
[paste_deploy]
flavor = keystone
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Image properties
~~~~~~~~~~~~~~~~
We recommend to use the following properties for your images:
- `` hw_scsi_model=virtio-scsi `` : add the virtio-scsi controller and get better performance and support for discard operation
- `` hw_disk_bus=scsi `` : connect every cinder block devices to that controller
- `` hw_qemu_guest_agent=yes `` : enable the QEMU guest agent
- `` os_require_quiesce=yes `` : send fs-freeze/thaw calls through the QEMU guest agent
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Configuring Cinder
------------------
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OpenStack requires a driver to interact with Ceph block devices. You must also
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specify the pool name for the block device. On your OpenStack node, edit
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`` /etc/cinder/cinder.conf `` by adding::
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[DEFAULT]
...
enabled_backends = ceph
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glance_api_version = 2
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...
[ceph]
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volume_driver = cinder.volume.drivers.rbd.RBDDriver
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volume_backend_name = ceph
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rbd_pool = volumes
rbd_ceph_conf = /etc/ceph/ceph.conf
rbd_flatten_volume_from_snapshot = false
rbd_max_clone_depth = 5
rbd_store_chunk_size = 4
rados_connect_timeout = -1
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If you are using `cephx authentication`_ , also configure the user and uuid of
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the secret you added to `` libvirt `` as documented earlier::
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[ceph]
...
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rbd_user = cinder
rbd_secret_uuid = 457eb676-33da-42ec-9a8c-9293d545c337
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Note that if you are configuring multiple cinder back ends,
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`` glance_api_version = 2 `` must be in the `` [DEFAULT] `` section.
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Configuring Cinder Backup
-------------------------
OpenStack Cinder Backup requires a specific daemon so don't forget to install it.
On your Cinder Backup node, edit `` /etc/cinder/cinder.conf `` and add::
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backup_driver = cinder.backup.drivers.ceph
backup_ceph_conf = /etc/ceph/ceph.conf
backup_ceph_user = cinder-backup
backup_ceph_chunk_size = 134217728
backup_ceph_pool = backups
backup_ceph_stripe_unit = 0
backup_ceph_stripe_count = 0
restore_discard_excess_bytes = true
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Configuring Nova to attach Ceph RBD block device
------------------------------------------------
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In order to attach Cinder devices (either normal block or by issuing a boot
from volume), you must tell Nova (and libvirt) which user and UUID to refer to
when attaching the device. libvirt will refer to this user when connecting and
authenticating with the Ceph cluster. ::
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[libvirt]
...
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rbd_user = cinder
rbd_secret_uuid = 457eb676-33da-42ec-9a8c-9293d545c337
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These two flags are also used by the Nova ephemeral backend.
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Configuring Nova
----------------
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In order to boot all the virtual machines directly into Ceph, you must
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configure the ephemeral backend for Nova.
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It is recommended to enable the RBD cache in your Ceph configuration file
(enabled by default since Giant). Moreover, enabling the admin socket
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brings a lot of benefits while troubleshooting. Having one socket
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per virtual machine using a Ceph block device will help investigating performance and/or wrong behaviors.
This socket can be accessed like this::
ceph daemon /var/run/ceph/ceph-client.cinder.19195.32310016.asok help
Now on every compute nodes edit your Ceph configuration file::
[client]
rbd cache = true
rbd cache writethrough until flush = true
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admin socket = /var/run/ceph/guests/$cluster-$type.$id.$pid.$cctid.asok
log file = /var/log/qemu/qemu-guest-$pid.log
rbd concurrent management ops = 20
Configure the permissions of these paths::
mkdir -p /var/run/ceph/guests/ /var/log/qemu/
chown qemu:libvirtd /var/run/ceph/guests /var/log/qemu/
Note that user `` qemu `` and group `` libvirtd `` can vary depending on your system.
The provided example works for RedHat based systems.
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.. tip :: If your virtual machine is already running you can simply restart it to get the socket
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Restart OpenStack
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=================
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To activate the Ceph block device driver and load the block device pool name
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into the configuration, you must restart OpenStack. Thus, for Debian based
systems execute these commands on the appropriate nodes::
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sudo glance-control api restart
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sudo service nova-compute restart
sudo service cinder-volume restart
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sudo service cinder-backup restart
For Red Hat based systems execute::
sudo service openstack-glance-api restart
sudo service openstack-nova-compute restart
sudo service openstack-cinder-volume restart
sudo service openstack-cinder-backup restart
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Once OpenStack is up and running, you should be able to create a volume
and boot from it.
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Booting from a Block Device
===========================
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You can create a volume from an image using the Cinder command line tool::
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cinder create --image-id {id of image} --display-name {name of volume} {size of volume}
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You can use `qemu-img`_ to convert from one format to another. For example::
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qemu-img convert -f {source-format} -O {output-format} {source-filename} {output-filename}
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qemu-img convert -f qcow2 -O raw precise-cloudimg.img precise-cloudimg.raw
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When Glance and Cinder are both using Ceph block devices, the image is a
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copy-on-write clone, so it can create a new volume quickly. In the OpenStack
dashboard, you can boot from that volume by performing the following steps:
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#. Launch a new instance.
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#. Choose the image associated to the copy-on-write clone.
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#. Select 'boot from volume'.
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#. Select the volume you created.
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.. _qemu-img: ../qemu-rbd/#running-qemu-with-rbd