Need to define default storage class

rook.md

@@ -87,3 +87,14 @@ rook-ceph-mds-myfs-b-dd78b444b-49h5h    1/1     Running   0          18s
 
 [21:07] server47.place7:~/ungleich-k8s/rook#
 ```
+
+## DefaultStorageClass
+
+By default none of the created storage classes are the "default" of
+the cluster. So we need to set one of them, if persistentvolumeclaims
+should be deployed:
+
+```
+[21:22] server47.place7:~/ungleich-k8s/rook# kubectl patch storageclass rook-ceph-block -p '{"metadata": {"annotations":{"stor
+ageclass.kubernetes.io/is-default-class":"true"}}}'
+```