Assuming an existing Proxmox cluster with node1, node2, node3 and node4:
node1, node2 and node3 are used as Ceph monitors, managers, MDSes and OSD nodes.
node4 is already in the Proxmox cluster, but is only used as a 'compute' node; pveceph is not installed.
So: node1 to node4 are in the...