Ceph Datastore

The Ceph Datastore driver allows the use of Ceph storage for images and disks of Virtual Machines.

Ceph Cluster Setup

This guide assumes that you already have a functional Ceph Cluster in place. Additionally you need to:

• Create a pool for the OpenNebula Datastores. Write down the name of the pool to include it in the datastore definitions.

$ ceph osd pool create one 128
$ ceph osd pool application enable one rbd
$ rbd pool init -p one
$ ceph osd lspools
0 data,1 metadata,2 rbd,6 one,

• Define a Ceph user to access the datastore pool; this user will also be used by libvirt to access the disk images. For example, create the user libvirt:

On the Ceph Jewel (v10.2.x and earlier):

$ ceph auth get-or-create client.libvirt \
      mon 'allow r' osd 'allow class-read object_prefix rbd_children, allow rwx pool=one'

On the Ceph Luminous (v12.2.x and later):

$ ceph auth get-or-create client.libvirt \
      mon 'profile rbd' osd 'profile rbd pool=one'

$ ceph auth caps client.libvirt \
      mon 'profile rbd' osd 'profile rbd pool=one'

* Get a copy of the key of this user to distribute it later to the OpenNebula Nodes.

```default
$ ceph auth get-key client.libvirt | tee client.libvirt.key

$ ceph auth get client.libvirt -o ceph.client.libvirt.keyring

• Although RBD format 1 is supported it is strongly recommended to use Format 2. Check that ceph.conf includes:

[global]
rbd_default_format = 2

• Pick a set of client nodes of the cluster to act as storage bridges. These nodes will be used to import images into the Ceph Cluster from OpenNebula. These nodes must have the qemu-img command installed.

Front-end and Hosts Setup

In order to use the Ceph Cluster the Hosts need to be configured as follows:

• The Ceph client tools must be available in the machine.
• The mon daemon must be defined in the ceph.conf for all the nodes, so hostname and port doesn’t need to be specified explicitly in any Ceph command.
• Copy the Ceph user keyring (ceph.client.libvirt.keyring) to the nodes under /etc/ceph, and the user key (client.libvirt.key) to the oneadmin home.

$ scp ceph.client.libvirt.keyring root@node:/etc/ceph

$ scp client.libvirt.key oneadmin@node:

Hosts Setup

Hosts need extra steps to set up credentials in libvirt:

• Generate a secret for the Ceph user and copy it to the nodes under oneadmin home. Write down the UUID for later use:

$ UUID=`uuidgen`; echo $UUID
c7bdeabf-5f2a-4094-9413-58c6a9590980

$ cat > secret.xml <<EOF
<secret ephemeral='no' private='no'>
  <uuid>$UUID</uuid>
  <usage type='ceph'>
          <name>client.libvirt secret</name>
  </usage>
</secret>
EOF

$ scp secret.xml oneadmin@node:

• Define a libvirt secret and remove key files in the nodes:

$ virsh -c qemu:///system secret-define secret.xml

$ virsh -c qemu:///system secret-set-value --secret $UUID --base64 $(cat client.libvirt.key)

$ rm client.libvirt.key

• The oneadmin account needs to access the Ceph Cluster using the libvirt Ceph user defined above. This requires access to the Ceph user keyring. Test that the Ceph client is properly configured in the node:

$ ssh oneadmin@node

$ rbd ls -p one --id libvirt

You can read more information about this in the Ceph guide Using libvirt with Ceph.

• Ancillary Virtual Machine files like context disks, deployment, and checkpoint files are created on the nodes under /var/lib/one/datastores/. Make sure that enough storage for these files is provisioned on the nodes.
• If you are going to use the SSH mode, you have to take into account the space needed for the System Datastore /var/lib/one/datastores/<ds_id> where ds_id is the ID of the System Datastore.

LXC Hosts

The rbd-nbd utility must be installed on LXC hosts. Check the LXC Node Installation.

OpenNebula Configuration

To use your Ceph Cluster with the OpenNebula, you need to define both System and Image Datastores. Each Image/System Datastore pair will share the following same Ceph configuration attributes:

$ sudo mv /etc/ceph/ceph.conf /etc/ceph/ceph1.conf

$ sudo grep -o -P '(?<=key = ).*(?=)' /etc/ceph/ceph.client.oneadmin.keyring >> /etc/ceph/ceph.client.oneadmin.key

$ onedatastore update <DS_ID>
CEPH_CONF="/etc/ceph/ceph1.conf"
CEPH_KEY="/etc/ceph/ceph.client.oneadmin.key"

Create System Datastore

System Datastore also requires these attributes:

Create a System Datastore in Sunstone or through the CLI, for example:

$ cat systemds.txt
NAME    = ceph_system
TM_MAD  = ceph
TYPE    = SYSTEM_DS
DISK_TYPE = RBD

POOL_NAME   = one
CEPH_HOST   = "host1 host2:port2"
CEPH_USER   = libvirt
CEPH_SECRET = "6f88b54b-5dae-41fe-a43e-b2763f601cfc"

BRIDGE_LIST = cephfrontend

$ onedatastore create systemds.txt
ID: 101

Create Image Datastore

Apart from the previous attributes, which need to be the same as the associated System Datastore, the following can be set for an Image Datastore:

An example of datastore:

> cat ds.conf
NAME = "cephds"
DS_MAD = ceph
TM_MAD = ceph

DISK_TYPE = RBD

POOL_NAME   = one
CEPH_HOST   = "host1 host2:port2"
CEPH_USER   = libvirt
CEPH_SECRET = "6f88b54b-5dae-41fe-a43e-b2763f601cfc"

BRIDGE_LIST = cephfrontend

> onedatastore create ds.conf
ID: 101

Additional Configuration

Default values for the Ceph drivers can be set in /var/lib/one/remotes/etc/datastore/ceph/ceph.conf:

• POOL_NAME: Default volume group.
• STAGING_DIR: Default path for image operations in the storage bridges.
• RBD_FORMAT: Default format for RBD volumes.
• DD_BLOCK_SIZE: Block size for dd operations (default: 64kB).
• SUPPORTED_FS: Comma-separated list with every file system supported for creating formatted datablocks. Can be set in /var/lib/one/remotes/etc/datastore/datastore.conf.
• FS_OPTS_<FS>: Options for creating the file system for formatted datablocks. Can be set in /var/lib/one/remotes/etc/datastore/datastore.conf for each file system type.

Using different modes

When creating a VM Template you can choose to deploy the disks using the default Ceph mode or the SSH one. Note that the same mode will be used for all disks of the VM. To set the deployment mode, add the following attribute to the VM template:

• TM_MAD_SYSTEM="ssh"

When using Sunstone, the deployment mode needs to be set in the Storage tab.

Datastore Internals

Images are stored in a Ceph pool, named after its OpenNebula ID one-<IMAGE ID>. Virtual Machine disks are stored by default in the same pool (Ceph Mode). You can also choose to export the Image rbd to the hypervisor local storage using the SSH Mode.

Ceph Mode (Default)

In this mode, Virtual Machines will use the same Image rbd volumes for their disks (persistent images), or a new snapshots of the image created in the form one-<IMAGE ID>-<VM ID>-<DISK ID> (non-persistent images).

For example, consider a system using an Image and System Datastore backed by a Ceph pool named one. The pool with one Image (ID 0) and two Virtual Machines 14 and 15 using this Image as virtual disk 0 would be similar to:

$ rbd ls -l -p one --id libvirt
NAME         SIZE PARENT         FMT PROT LOCK
one-0      10240M                  2
one-0@snap 10240M                  2 yes
one-0-14-0 10240M one/one-0@snap   2
one-0-15-0 10240M one/one-0@snap   2

SSH Mode

In this mode, the associated rbd file for each disk is exported to a file and stored in the local file system of the hypervisor.

For instance, in the previous example, if the VM 14 is set to be deployed in an SSH System Datastore (e.g., 100), the layout of the datastore in the hypervisor would be similar to:

$ ls -l /var/lib/one/datastores/100/14
total 609228
-rw-rw-r-- 1 oneadmin oneadmin        1020 Dec 20 14:41 deployment.0
-rw-r--r-- 1 oneadmin oneadmin 10737418240 Dec 20 15:19 disk.0
-rw-rw-r-- 1 oneadmin oneadmin      372736 Dec 20 14:41 disk.1

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