diff --git a/doc/source/user/index.rst b/doc/source/user/index.rst
index 3195c9a508..a22b659dea 100644
--- a/doc/source/user/index.rst
+++ b/doc/source/user/index.rst
@@ -213,8 +213,9 @@ They are loosely grouped as: mandatory, infrastructure, COE specific.
   If specified, container images will be stored in a cinder volume of the
   specified size in GB. Each cluster node will have a volume attached of
   the above size. If not specified, images will be stored in the compute
-  instance's local disk. For the 'devicemapper' storage driver, the minimum
-  value is 3GB. For the 'overlay' storage driver, the minimum value is 1GB.
+  instance's local disk. For the 'devicemapper' storage driver, must specify
+  volume and the minimum value is 3GB. For the 'overlay' and 'overlay2'
+  storage driver, the minimum value is 1GB or None(no volume).
   This value can be overridden at cluster creation.
 
 --docker-storage-driver \<docker-storage-driver\>
diff --git a/magnum/api/validation.py b/magnum/api/validation.py
index a7c6a4f306..5c028e796d 100644
--- a/magnum/api/validation.py
+++ b/magnum/api/validation.py
@@ -205,11 +205,10 @@ def _enforce_volume_driver_types(cluster_template):
 def _enforce_volume_storage_size(cluster_template, cluster):
     volume_size = cluster.get('docker_volume_size') \
         or cluster_template.get('docker_volume_size')
-    if not volume_size:
-        return
     storage_driver = cluster_template.get('docker_storage_driver')
+
     if storage_driver == 'devicemapper':
-        if volume_size < 3:
+        if not volume_size or volume_size < 3:
             raise exception.InvalidParameterValue(
                 'docker volume size %s GB is not valid, '
                 'expecting minimum value 3GB for %s storage '