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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  2.8.1    unsupported  19:34:16Z

App          Version  Status  Scale  Charm     Store       Rev  OS      Notes
ceph-client  20.04    active      1  ubuntu    jujucharms   15  ubuntu
ceph-mon     15.2.3   active      3  ceph-mon  jujucharms   49  ubuntu  
ceph-osd     15.2.3   active      3  ceph-osd  jujucharms  304  ubuntu  

Unit            Workload  Agent  Machine  Public address  Ports  Message
ceph-client/0*  active    idle   3             ready
ceph-mon/0      active    idle   0/lxd/1             Unit is ready and clustered
ceph-mon/1      active    idle   1/lxd/1             Unit is ready and clustered
ceph-mon/2*     active    idle   2/lxd/1             Unit is ready and clustered
ceph-osd/0      active    idle   0             Unit is ready (2 OSD)
ceph-osd/1*     active    idle   1             Unit is ready (2 OSD)
ceph-osd/2      active    idle   2             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-action --wait ceph-mon/0 create-pool name=libvirt-pool app-name=rbd

juju run --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

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