code: protected void writeInputData(long genbytes, Path ioPath)
        throws IOException, InterruptedException {
      final Configuration conf = getConf();
      final GridmixJob genData = new GenerateData(conf, ioPath, genbytes);
      submitter.add(genData);
      LOG.info("Generating " + StringUtils.humanReadableInt(genbytes) +
          " of test data...");
      // TODO add listeners, use for job dependencies
      TimeUnit.SECONDS.sleep(10);
      try {
        genData.getJob().waitForCompletion(false);
      } catch (ClassNotFoundException e) {
        throw new IOException("Internal error", e);
      }
      if (!genData.getJob().isSuccessful()) {
        throw new IOException("Data generation failed!");
      }
      LOG.info("Done.");
    }
docs: Write random bytes at the path provided.
  @see org.apache.hadoop.mapred.gridmix.GenerateData