@Override
  public void sync() throws IOException {
    for (int i = 0; i < fileChannels.length; i++) {
      try {
        if (fileChannels[i] != null) {
          fileChannels[i].force(true);
        }
      } catch (IOException ie) {
        LOG.warn("Failed syncing data to " + this.filePaths[i]);
        throw ie;
      }
    }
  }
Sync the data to file after writing
hbase-server/src/main/java/org/apache/hadoop/hbase/io/hfile/bucket/FileIOEngine.java