roles:
- [mon.a, mgr.y, mds.a, osd.0, osd.1, osd.2, osd.3, client.0]
- [mon.b, mon.c, mgr.x, mds.b, osd.4, osd.5, osd.6, osd.7, client.1]
openstack:
- volumes: # attached to each instance
    count: 4
    size: 20 # GB
- machine:
    disk: 200 # GB