code: public void populateSaving(RaidNodeMetrics metrics) {
      if (lastRaidStatistics == null) {
        return;
      }
      long saving = 0;
      for (Codec codec : Codec.getCodecs()) {
        String code = codec.id;
        long s = lastRaidStatistics.get(code).getSaving(conf);
        if (s > 0) {
          metrics.savingForCode.get(code).set(s);
          saving += s;
        }
      }
      if (saving > 0) {
        metrics.saving.set(saving);
      }
    }
docs: Populate RAID savings by code and total.
  @return Number of bytes saved due to RAID