code: public void mergeInternal(INode parityINodes[], INode sourceINodes[],
        String parity, String source, RaidCodec codec, int[] checksums)
            throws IOException {
      waitForReady();
      long now = FSNamesystem.now();
      unprotectedMerge(parityINodes, sourceINodes, parity, source, codec,
          checksums, now);
      fsImage.getEditLog().logMerge(parity, source, codec.id, checksums, now);
    }
docs: Merge all the blocks in the parity file into source file.
  Source file will be converted into INodeRaidStorage format to include both
  parity blocks and source blocks