From the ceph doc :
librbd supports limiting per image IO, controlled by the following settings.
Running the commands from the doc prints unknown options qos ....
I haven't found anything on the web so far. Can anyone help me please?
I've finally found the correct command here. I'm posting it here hoping it helps someone in the future.
At the image level:
rbd config image set <pool>/<image> rbd_qos_iops_limit <value>
At the pool level:
rbd config pool set <pool> rbd_qos_iops_limit <value>