code: public long getSaving() {
      if (lastRaidStatistics == null) {
        return -1;
      }
      long saving = 0;
      for (Codec codec : Codec.getCodecs()) {
        String code = codec.id;
        long s = lastRaidStatistics.get(code).getSaving(conf);
        if (s == -1) {
          return -1;
        }
        saving += s;
      }
      return saving;
    }
docs: Get the total RAID saving in bytes
  @return Number of bytes saved due to RAID