juju add-model ceph
juju model-config default-series=focal
juju deploy --config osd-devices=/dev/vdb ceph-osd
juju deploy --config monitor-count=1 ceph-mon
juju add-relation ceph-osd:mon ceph-mon:osd

juju status --relations

Model  Controller  Cloud/Region    Version  SLA          Timestamp
ceph   maas-one    mymaas/default  2.8.0    unsupported  22:30:25Z

App       Version  Status   Scale  Charm     Store       Rev  OS      Notes
ceph-mon  15.2.1   waiting      1  ceph-mon  jujucharms   48  ubuntu  
ceph-osd  15.2.1   active       1  ceph-osd  jujucharms  303  ubuntu  

Unit         Workload  Agent  Machine  Public address  Ports  Message
ceph-mon/0*  waiting   idle   1        10.0.0.174             Monitor bootstrapped but waiting for number of OSDs to reach expected-osd-count (3)
ceph-osd/0*  active    idle   0        10.0.0.173             Unit is ready (1 OSD)

Machine  State    DNS         Inst id  Series  AZ       Message
0        started  10.0.0.173  node1    focal   default  Deployed
1        started  10.0.0.174  node2    focal   default  Deployed

Relation provider  Requirer      Interface  Type     Message
ceph-mon:mon       ceph-mon:mon  ceph       peer     
ceph-mon:osd       ceph-osd:mon  ceph-osd   regular

juju config ceph-mon expected-osd-count
0