Query: ibm_compute_instance_disk_by_instance_state

   with disks as (
     select
       case
         when i.status <> 'running' then 'unused'
         else 'in-use' 
	  end as state
	from
		ibm_is_instance_disk as d,
		ibm_is_instance as i
	where
		d.instance_id = i.id
)
   select
     state,
     count(*)
   from
     disks
   group by
     state;