// +optional
  repeated string accessModes = 3;

  // claimRef is part of a bi-directional binding between PersistentVolume and PersistentVolumeClaim.
  // Expected to be non-nil when bound.
  // claim.VolumeName is the authoritative bind between PV and PVC.
  // More info: https://kubernetes.io/docs/concepts/storage/persistent-volumes#binding
  // +optional
  // +structType=granular
  optional ObjectReference claimRef = 4;