Block storage

Ceph block storage interacts directly with RADOS and a separate daemon is therefore not required (unlike CephFS and RGW). A Ceph block device is known as a RADOS Block Device (or simply an RBD device) and is available from a newly deployed Ceph cluster. This also makes RBD highly available by default.

RBD client usage

This section will provide optional instructions for verifying the RBD service by setting up a simple client environment. Deploy the client using the steps provided in the Client setup appendix.

An example deployment will have a juju status output similar to the following:

Model Controller Cloud/Region Version SLA Timestamp
ceph my-controller my-maas/default 3.5.2 unsupported 20:34:16Z
App Version Status Scale Charm Channel Rev OS Notes
ceph-mon 18.2.0 active 3 ceph-mon reef/stable 93 ubuntu 
ceph-osd 18.2.0 active 3 ceph-osd reef/stable 528 ubuntu
ceph-client 22.04 active 1 ubuntu stable 18 ubuntu 
Unit Workload Agent Machine Public address Ports Message
ceph-client/0* active idle 3 10.0.0.240 ready
ceph-mon/0 active idle 0/lxd/1 10.0.0.247 Unit is ready and clustered
ceph-mon/1 active idle 1/lxd/1 10.0.0.242 Unit is ready and clustered
ceph-mon/2* active idle 2/lxd/1 10.0.0.249 Unit is ready and clustered
ceph-osd/0 active idle 0 10.0.0.229 Unit is ready (2 OSD)
ceph-osd/1* active idle 1 10.0.0.230 Unit is ready (2 OSD)
ceph-osd/2 active idle 2 10.0.0.252 Unit is ready (2 OSD)

The client host is represented by the ceph-client/0 unit.

Create a Ceph pool (‘libvirt-pool’), an RBD user (‘client.libvirt’), collect the user’s keyring file, and transfer it to the client:

juju run --wait ceph-mon/0 create-pool name=libvirt-pool app-name=rbd
juju exec --unit ceph-mon/0 -- \
 sudo ceph auth get-or-create client.libvirt \
 mon 'profile rbd' osd 'profile rbd pool=libvirt-pool' | \
 tee ceph.client.libvirt.keyring
juju scp ceph.client.libvirt.keyring ceph-client/0:

Connect to the client:

juju ssh ceph-client/0

From the RBD client,

Configure the client using the keyring file and set up the correct permissions:

sudo mv ~ubuntu/ceph.client.libvirt.keyring /etc/ceph
sudo chmod 600 /etc/ceph/ceph.client.libvirt.keyring
sudo chown ubuntu: /etc/ceph/ceph.client.libvirt.keyring

Install the requisite image creation software and verify that an RBD image can be created:

sudo apt install -y qemu-utils
qemu-img create -f raw rbd:libvirt-pool/image-4d:id=libvirt 4G

From the Juju client,

RBD images/pools can be inspected by querying the cluster with various commands:

juju ssh ceph-mon/0 sudo rbd -p libvirt-pool ls
juju ssh ceph-mon/0 sudo rados df --pool libvirt-pool