code: @Override
    protected boolean isGoodTarget(DatanodeDescriptor node,
                                   long blockSize,
                                   int maxPerRack,
                                   boolean considerLoad,
                                   List<DatanodeDescriptor> results) {
      if (badRacks.contains(node.getNetworkLocation()) ||
          badHosts.contains(node.getName())) {
        return false;
      }
      return super.isGoodTarget(
        node, blockSize, maxPerRack, considerLoad, results);
    }
docs: / A helper function that says some hosts are bad based on test config.