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339 lines
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ReStructuredText
339 lines
13 KiB
ReStructuredText
=============================
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Block Devices and OpenStack
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=============================
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.. index:: Ceph Block Device; OpenStack
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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
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quad-core processor. The following diagram depicts the OpenStack/Ceph
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technology stack.
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.. ditaa:: +---------------------------------------------------+
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| OpenStack |
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+---------------------------------------------------+
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| libvirt |
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+------------------------+--------------------------+
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| configures
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v
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+---------------------------------------------------+
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| QEMU |
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+---------------------------------------------------+
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| librbd |
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+---------------------------------------------------+
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| librados |
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+------------------------+-+------------------------+
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| OSDs | | Monitors |
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+------------------------+ +------------------------+
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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,
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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
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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
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advantageous because it allows you to perform maintenance operations easily
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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
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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
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while running VMs using a local disk, or vice versa.
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.. important:: Ceph doesn’t support QCOW2 for hosting a virtual machine disk.
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Thus if you want to boot virtual machines in Ceph (ephemeral backend or boot
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from volume), the Glance image format must be ``RAW``.
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.. tip:: This document describes using Ceph Block Devices with OpenStack Havana.
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For earlier versions of OpenStack see
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`Block Devices and OpenStack (Dumpling)`_.
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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
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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
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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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.. _Create a Pool: ../../rados/operations/pools#createpool
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.. _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
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``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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----------------------------
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On the ``glance-api`` node, you'll need the Python bindings for ``librbd``::
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sudo apt-get install python-ceph
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sudo yum install python-ceph
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On the ``nova-compute``, ``cinder-backup`` and on the ``cinder-volume`` node,
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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
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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.cinder mon 'allow r' osd 'allow class-read object_prefix rbd_children, allow rwx pool=volumes, allow rwx pool=vms, allow rx pool=images'
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ceph auth get-or-create client.glance mon 'allow r' osd 'allow class-read object_prefix rbd_children, allow rwx pool=images'
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ceph auth get-or-create client.cinder-backup mon 'allow r' osd 'allow class-read object_prefix rbd_children, allow rwx pool=backups'
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Add the keyrings for ``client.cinder``, ``client.glance``, and
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``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
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ssh {your-glance-api-server} sudo chown glance:glance /etc/ceph/ceph.client.glance.keyring
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ceph auth get-or-create client.cinder | ssh {your-volume-server} sudo tee /etc/ceph/ceph.client.cinder.keyring
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ssh {your-cinder-volume-server} sudo chown cinder:cinder /etc/ceph/ceph.client.cinder.keyring
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ceph auth get-or-create client.cinder-backup | ssh {your-cinder-backup-server} sudo tee /etc/ceph/ceph.client.cinder-backup.keyring
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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. 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
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a block device from Cinder.
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Create a temporary copy of the secret key on the nodes running
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``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
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457eb676-33da-42ec-9a8c-9293d545c337
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cat > secret.xml <<EOF
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<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>
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</secret>
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EOF
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sudo virsh secret-define --file secret.xml
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Secret 457eb676-33da-42ec-9a8c-9293d545c337 created
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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.
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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/operations/authentication
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Configure OpenStack to use Ceph
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===============================
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Configuring Glance
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------------------
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Glance can use multiple back ends to store images. To use Ceph block devices by
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default, edit ``/etc/glance/glance-api.conf`` and add::
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default_store=rbd
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rbd_store_user=glance
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rbd_store_pool=images
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If you want to enable copy-on-write cloning of images, also add::
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show_image_direct_url=True
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Note that this exposes the back end location via Glance's API, so the endpoint
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with this option enabled should not be publicly accessible.
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Configuring Cinder
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------------------
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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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volume_driver=cinder.volume.drivers.rbd.RBDDriver
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rbd_pool=volumes
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rbd_ceph_conf=/etc/ceph/ceph.conf
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rbd_flatten_volume_from_snapshot=false
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rbd_max_clone_depth=5
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glance_api_version=2
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If you're 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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rbd_user=cinder
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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
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-------------------------
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OpenStack Cinder Backup requires a specific daemon so don't forget to install it.
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On your Cinder Backup node, edit ``/etc/cinder/cinder.conf`` and add::
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backup_driver=cinder.backup.drivers.ceph
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backup_ceph_conf=/etc/ceph/ceph.conf
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backup_ceph_user=cinder-backup
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backup_ceph_chunk_size=134217728
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backup_ceph_pool=backups
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backup_ceph_stripe_unit=0
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backup_ceph_stripe_count=0
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restore_discard_excess_bytes=true
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Configuring Nova to attach Ceph RBD block device
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------------------------------------------------
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In order to attach Cinder devices (either normal block or by issuing a boot
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from volume), you must tell Nova (and libvirt) which user and UUID to refer to
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when attaching the device. libvirt will refer to this user when connecting and
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authenticating with the Ceph cluster. ::
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rbd_user=cinder
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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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----------------
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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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Havana and Icehouse require patches to implement copy-on-write cloning and fix
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bugs with image size and live migration of ephemeral disks on rbd. These are
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available in branches based on upstream Nova `stable/havana`_ and
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`stable/icehouse`_. Using them is not mandatory but **highly recommended** in
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order to take advantage of the copy-on-write clone functionality.
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On every Compute node, edit ``/etc/nova/nova.conf`` and add::
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libvirt_images_type=rbd
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libvirt_images_rbd_pool=vms
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libvirt_images_rbd_ceph_conf=/etc/ceph/ceph.conf
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rbd_user=cinder
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rbd_secret_uuid=457eb676-33da-42ec-9a8c-9293d545c337
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It is also a good practice to disable file injection. While booting an
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instance, Nova usually attempts to open the rootfs of the virtual machine.
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Then, Nova injects values such as password, ssh keys etc. directly into the
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filesystem. However, it is better to rely on the metadata service and
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``cloud-init``.
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On every Compute node, edit ``/etc/nova/nova.conf`` and add::
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libvirt_inject_password=false
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libvirt_inject_key=false
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libvirt_inject_partition=-2
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To ensure a proper live-migration, use the following flags::
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libvirt_live_migration_flag="VIR_MIGRATE_UNDEFINE_SOURCE,VIR_MIGRATE_PEER2PEER,VIR_MIGRATE_LIVE,VIR_MIGRATE_PERSIST_DEST"
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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
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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
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sudo service cinder-volume restart
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sudo service cinder-backup restart
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For Red Hat based systems execute::
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sudo service openstack-glance-api restart
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sudo service openstack-nova-compute restart
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sudo service openstack-cinder-volume restart
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sudo service openstack-cinder-backup restart
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Once OpenStack is up and running, you should be able to create a volume
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and boot from it.
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Booting from a Block Device
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===========================
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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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Note that image must be RAW format. You can use `qemu-img`_ to convert
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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
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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
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.. _Block Devices and OpenStack (Dumpling): http://ceph.com/docs/dumpling/rbd/rbd-openstack
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.. _stable/havana: https://github.com/jdurgin/nova/tree/havana-ephemeral-rbd
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.. _stable/icehouse: https://github.com/angdraug/nova/tree/rbd-ephemeral-clone-stable-icehouse
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