// meant to be used by the pod, the PVC has to updated with an
  // owner reference to the pod once the pod exists. Normally
  // this should not be necessary, but it may be useful when
  // manually reconstructing a broken cluster.
  //
  // This field is read-only and no changes will be made by Kubernetes
  // to the PVC after it has been created.
  //
  // Required, must not be nil.