diff --git a/zaza/openstack/charm_tests/ceph/tests.py b/zaza/openstack/charm_tests/ceph/tests.py
index 61c2d47..5bede4a 100644
--- a/zaza/openstack/charm_tests/ceph/tests.py
+++ b/zaza/openstack/charm_tests/ceph/tests.py
@@ -552,13 +552,13 @@ class CephTest(test_utils.OpenStackBaseTest):
         return int(result['num_osds'])
 
     def test_cache_device(self):
-        """Test adding a new disk with a caching device."""
+    """Test adding a new disk with a caching device."""
         logging.info('Running add-disk action with a caching device')
+        mon = next(iter(zaza_model.get_units('ceph-mon'))).entity_id
         osds = [x.entity_id for x in zaza_model.get_units('ceph-osd')]
-        num_osds = self.get_num_osds(osds[0])
         for unit in osds:
-            zaza_model.add_storage(unit, 'cache-devices', 'cinder', 10)
-            loop_dev = zaza_utils.add_loop_device(unit, 10)
+            add_storage(unit, 'cache-devices', 'cinder', 10)
+            loop_dev = add_loop_device(unit, 10)
             action_obj = zaza_model.run_action(
                 unit_name=unit,
                 action_name='add-disk',
@@ -566,7 +566,7 @@ class CephTest(test_utils.OpenStackBaseTest):
                                'partition-size': 5}
             )
             zaza_utils.assertActionRanOK(action_obj)
-        self.assertEqual(num_osds + len(osds), self.get_num_osds(osds[0]))
+        self.assertEqual(len(osds) * 2, self.get_num_osds(mon))
 
 
 class CephRGWTest(test_utils.OpenStackBaseTest):