Bug fix for free space calculation

Instead of calculating the free space ourselves, simply report the
amount of free space that the storage array tells us it has.

Closes-bug: #1918229
Change-Id: Iff02775822056904e5457ecddcefb2e580f47953

cinder/tests/unit/volume/drivers/test_nimble.py

@@ -197,9 +197,7 @@ FAKE_POSITIVE_GROUP_INFO_RESPONSE = {
     'name': 'group-nimble',
     'usage_valid': True,
     'usable_capacity_bytes': 8016883089408,
-    'compressed_vol_usage_bytes': 2938311843,
-    'compressed_snap_usage_bytes': 36189,
-    'unused_reserve_bytes': 0}
+    'free_space': 101111111901}
 
 FAKE_GET_VOL_INFO_RESPONSE = {'name': 'testvolume-cg',
                               'clone': False,
@@ -1136,7 +1134,7 @@ class NimbleDriverVolumeTestCase(NimbleDriverBaseTestCase):
                         'storage_protocol': 'iSCSI',
                         'pools': [{'pool_name': 'NIMBLE',
                                    'total_capacity_gb': 7466.30419921875,
-                                   'free_capacity_gb': 7463.567649364471,
+                                   'free_capacity_gb': 94.16706105787307,
                                    'reserved_percentage': 0,
                                    'QoS_support': False,
                                    'multiattach': True,

cinder/volume/drivers/nimble.py

@@ -382,15 +382,11 @@ class NimbleBaseVolumeDriver(san.SanDriver):
                                               'array is invalid'))
             total_capacity = (group_info['usable_capacity_bytes'] /
                               float(units.Gi))
-            used_space = ((group_info['compressed_vol_usage_bytes'] +
-                          group_info['compressed_snap_usage_bytes'] +
-                          group_info['unused_reserve_bytes']) /
+            free_space = (group_info['free_space'] /
                           float(units.Gi))
-            free_space = total_capacity - used_space
             LOG.debug('total_capacity=%(capacity)f '
-                      'used_space=%(used)f free_space=%(free)f',
+                      'free_space=%(free)f',
                       {'capacity': total_capacity,
-                       'used': used_space,
                        'free': free_space})
 
             backend_name = self.configuration.safe_get(

releasenotes/notes/bug-1918229-0aa9fd75c5e843d5.yaml

@@ -0,0 +1,8 @@
+---
+fixes:
+  - |
+    Nimble driver `bug #1918229
+    <https://bugs.launchpad.net/cinder/+bug/1918229>`_: Corrected an issue
+    where the Nimble storage driver was inaccurately determining that there
+    was no free space left in the storage array. The driver now relies on the
+    storage array to report the amount of free space.