diff --git a/lib/ansible/modules/system/vdo.py b/lib/ansible/modules/system/vdo.py
index 9fe009c3f2b..6a970cb9c33 100644
--- a/lib/ansible/modules/system/vdo.py
+++ b/lib/ansible/modules/system/vdo.py
@@ -127,6 +127,7 @@ options:
               volumes will maintain their previously configured
               setting unless a different value is specified in the
               playbook.
+            - The read cache feature is available in VDO 6.1 and older.
         type: str
         choices: [ disabled, enabled ]
     readcachesize:
@@ -142,6 +143,7 @@ options:
               Existing volumes will maintain their previously
               configured setting unless a different value is specified
               in the playbook.
+            - The read cache feature is available in VDO 6.1 and older.
         type: str
     emulate512:
         description: