diff --git a/cinder/db/sqlalchemy/migrate_repo/versions/097_enforce_ocata_online_migrations.py b/cinder/db/sqlalchemy/migrate_repo/versions/097_enforce_ocata_online_migrations.py
new file mode 100644
index 00000000000..a0b91acef4c
--- /dev/null
+++ b/cinder/db/sqlalchemy/migrate_repo/versions/097_enforce_ocata_online_migrations.py
@@ -0,0 +1,50 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+from sqlalchemy import MetaData, Table, func, select
+
+from cinder import exception
+from cinder.i18n import _
+
+
+WARNING_MSG = _('There are still %(count)i unmigrated records in '
+                'the %(table)s table. Migration cannot continue '
+                'until all records have been migrated.')
+
+
+def upgrade(migrate_engine):
+    meta = MetaData(migrate_engine)
+
+    # CGs to Generic Volume Groups transition
+    consistencygroups = Table('consistencygroups', meta, autoload=True)
+    cgsnapshots = Table('cgsnapshots', meta, autoload=True)
+    for table in (consistencygroups, cgsnapshots):
+        count = select([func.count()]).select_from(table).where(
+            table.c.deleted == False).execute().scalar()  # NOQA
+        if count > 0:
+            msg = WARNING_MSG % {
+                'count': count,
+                'table': table.name,
+            }
+            raise exception.ValidationError(detail=msg)
+
+    # VOLUME_ prefix addition in message IDs
+    messages = Table('messages', meta, autoload=True)
+    count = select([func.count()]).select_from(messages).where(
+        (messages.c.deleted == False) &
+        (~messages.c.event_id.like('VOLUME_%'))).execute().scalar()  # NOQA
+    if count > 0:
+        msg = WARNING_MSG % {
+            'count': count,
+            'table': 'messages',
+        }
+        raise exception.ValidationError(detail=msg)
diff --git a/cinder/exception.py b/cinder/exception.py
index 72b394d60bd..1f278fda334 100644
--- a/cinder/exception.py
+++ b/cinder/exception.py
@@ -277,6 +277,10 @@ class MissingRequired(Invalid):
     message = _("Missing required element '%(element)s' in request body.")
 
 
+class ValidationError(Invalid):
+    message = "%(detail)s"
+
+
 class APIException(CinderException):
     message = _("Error while requesting %(service)s API.")