How to monitor docker storage size as a OpenShift admin?

Issue

• oc describe node shows the capacity of cpu, memory and pods. But it doesn't report docker storage size.

$ oc describe node knakayam-ose33-node1.example.com
  ...
Capacity:
 alpha.kubernetes.io/nvidia-gpu:    0
 cpu:                   2
 memory:                3881816Ki
 pods:                  110
  ...