code: void wipeDatanode(DatanodeID nodeID) throws IOException {
      String key = nodeID.getStorageID();
      host2DataNodeMap.remove(datanodeMap.remove(key));
      if (NameNode.stateChangeLog.isDebugEnabled()) {
        NameNode.stateChangeLog.debug(
          "BLOCK* NameSystem.wipeDatanode: "
            + nodeID.getName() + " storage " + key
            + " is removed from datanodeMap.");
      }
    }
docs: Physically remove node from datanodeMap.
  
  @param nodeID node