code: public DiskStatus getNSDiskStatus() throws IOException {
      long rawNums[] = namenode.getStats();
      // rawNums[6] should be capacityNamespaceUsed
      long dfsUsed = (rawNums.length > 6)? rawNums[6]: rawNums[1];
      return new DiskStatus(rawNums[0], dfsUsed, rawNums[2]);
    }
docs: /*
  Return the Disk status for current namespace