code: private void genFile(Path file, long fileSize) throws IOException {
      long startTime = System.currentTimeMillis();
      FSDataOutputStream out = fs.create(file, true,
          getConf().getInt("io.file.buffer.size", 4096),
          (short)getConf().getInt("dfs.replication", 3),
          fs.getDefaultBlockSize());
      executionTime[CREATE] += (System.currentTimeMillis()-startTime);
      totalNumOfOps[CREATE]++;
  
      for (long i=0; i<fileSize; i++) {
        out.writeByte('a');
      }
      startTime = System.currentTimeMillis();
      out.close();
      executionTime[WRITE_CLOSE] += (System.currentTimeMillis()-startTime);
      totalNumOfOps[WRITE_CLOSE]++;
    }
docs: Create a file with a length of <code>fileSize</code>.
  The file is filled with 'a'.