[Pure Storage] Resolve EG1 arrays not reporting DRR

FlashArrays using the EG1 subscription model do not report
array data reduction rates, which caused a failure in reporting
array stats back to cinder.

This patch fixes this by forcing EG1 arrays to use the classic
non-dynamic oversubscription calculations in Cinder.

Closes-Bug: #2119222
Change-Id: Id6bfa990bc5f302b39807e7ea90d38007a5b327a
Signed-off-by: Simon Dodsley <simon@purestorage.com>

cinder/volume/drivers/pure.py

@@ -1248,7 +1248,13 @@ class PureBaseVolumeDriver(san.SanDriver):
         except AttributeError:
             provisioned_space = float(space_info.space.
                                       used_provisioned) / units.Gi
+        # If array uses Evergreen/One model then data reduction values
+        # are not reported so we must force the driver to use the old
+        # cinder non-dynamic oversubscription calculations
+        try:
             total_reduction = float(space_info.space.total_reduction)
+        except AttributeError:
+            total_reduction = 999
         total_vols = len(volumes)
         total_hosts = len(hosts)
         total_snaps = len(snaps)

releasenotes/notes/pure_eg1_dr-f08544454cfd105e.yaml

@@ -0,0 +1,7 @@
+---
+fixes:
+  - |
+    Pure Storage driver `Bug #2119222
+    <https://bugs.launchpad.net/cinder/+bug/2119222>`_: Fixed
+    issue with EG1 subscription-based FlashArrays not reporting
+    data reduction rates.