code: public DatanodeInfo[] getDataNodeStats(final boolean useStandby)
      throws IOException {
      return new StandbyCaller<DatanodeInfo[]>() {
        @Override
        DatanodeInfo[] call(DistributedFileSystem fs) throws IOException {
          return fs.getDataNodeStats();
        }
      }.callFS(useStandby);
    }
docs: Return statistics for each datanode.
  @return array of data node reports
  @throw IOException