Opennebula doesn't control free space in SSH System Datastore

Opennebula doesn’t control free space in a host SSH System Datastore.
Because qcow2 file increases on demand, sometimes summary of limits disks size for all VM’s on the host can be greater than free disk space in host datastore.
May be it’s normal for most situation, but I have caught problems with end of free space in host’s System Datastore. I think it would be good, if I could enable strictly policy about disk space for some hosts like option(or vice versa).