public String getNextFolderForTsFile(int tierLevel, boolean sequence)
      throws DiskSpaceInsufficientException {
    return sequence
        ? seqTiers.get(tierLevel).getNextFolder()
        : unSeqTiers.get(tierLevel).getNextFolder();
  }
total space of each tier, Long.MAX_VALUE when one tier contains remote storage
iotdb-core/datanode/src/main/java/org/apache/iotdb/db/storageengine/rescon/disk/TierManager.java