code: public static boolean shouldRaid(Configuration conf, FileSystem srcFs, 
        FileStatus stat, Codec codec, List<FileStatus> lfs) throws IOException {
      Path p = stat.getPath();
      long blockNum = 0L;
      if (stat.isDir() != codec.isDirRaid) {
        return false;
      }
      
      if (tooNewForRaid(stat)) {
        return false;
      }
      
      blockNum = codec.isDirRaid ? 
          DirectoryStripeReader.getBlockNum(lfs) : numBlocks(stat);
      
      // if the file/directory has fewer than 2 blocks, then nothing to do
      if (blockNum <= RaidState.TOO_SMALL_NOT_RAID_NUM_BLOCKS) {
        return false;
      }
      
      return !raidedByOtherHighPriCodec(conf, stat, codec);
    }
docs: Decide whether a file/directory is too small to raid.