def METHOD_NAME(ceph_cluster):
    for mnode in ceph_cluster.get_nodes("mon"):
        if mnode.role == "mon":
            m = mnode.role
            log.info("%s" % m)
            out, rc = mnode.exec_command(cmd="sudo ceph df ")
            output = out.read()
            str = output.decode()
            print(str)
            l = []
            for s in str.split():
                if re.findall(r"-?\d+\.?\d*", s):
                    l.append(s)
            print(l[3])
            cluster_filled_perc = float(l[3])
            if cluster_filled_perc > 30:
                return 0
            return 1