Currently, storage_volumes (and thereby cimi volumes) include both system and additional disks with the fgcp.
The reason I included system disks was because it exposed the snapshot (backup & restore) operation for the system disk.
This is very apparent when listing system volumes: when creating a system from a template with only machine templates, no volume templates, the system volume collection includes the machines' system volumes, which just looks wrong.
Also, in a recent discussion on the DC dev ML with David L., it was clarified that system disks should not be included:
are these truly volumes (i.e., storage that as its own lifecycle, not
connected to that of the machine to which it is attached ?) If so, I
believe they should be included - if they vanish when the machine
vanishes, they are 'disks' not 'volumes' in CIMI lingo.