roles: - [mon.a, osd.0, osd.4, osd.8, osd.12] - [mon.b, osd.1, osd.5, osd.9, osd.13] - [mon.c, osd.2, osd.6, osd.10, osd.14] - [osd.3, osd.7, osd.11, osd.15, client.0]