2 - [mon.a, mon.c, osd.0, osd.1, osd.2]
3 - [mon.b, mgr.x, mds.a, osd.3, osd.4, osd.5]
7 - volumes: # attached to each instance
15 test_image: 'test_image-0'
16 scratch_image: 'scratch_image-0'
20 test_image: 'test_image-1'
21 scratch_image: 'scratch_image-1'