boolean isOldEnough(FileStatus file) {
    return file.getModificationTime() + fileTtl < EnvironmentEdgeManager.currentTime();
  }
This Chore, every time it runs, will clear the unsused HFiles in the data folder.
hbase-server/src/main/java/org/apache/hadoop/hbase/regionserver/BrokenStoreFileCleaner.java