public Map<String, List<DataRegionId>> getLocalDataRegionInfo() {
    File system = SystemFileFactory.INSTANCE.getFile(systemDir);
    File[] sgDirs = system.listFiles();
    Map<String, List<DataRegionId>> localDataRegionInfo = new HashMap<>();
    if (sgDirs == null) {
      return localDataRegionInfo;
    }
    for (File sgDir : sgDirs) {
      if (!sgDir.isDirectory()) {
        continue;
      }
      String sgName = sgDir.getName();
      List<DataRegionId> dataRegionIdList = new ArrayList<>();
      for (File dataRegionDir : Objects.requireNonNull(sgDir.listFiles())) {
        if (!dataRegionDir.isDirectory()) {
          continue;
        }
        dataRegionIdList.add(new DataRegionId(Integer.parseInt(dataRegionDir.getName())));
      }
      localDataRegionInfo.put(sgName, dataRegionIdList);
    }
    return localDataRegionInfo;
  }
get StorageGroup -> DataRegionIdList map from data/system directory.
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/StorageEngine.java