public void writeBackupStartCode(Long startCode) throws IOException {
    systemTable.writeBackupStartCode(startCode, backupInfo.getBackupRootDir());
  }
Write the start code (timestamp) to backup system table. If passed in null, then write 0 byte.
@param startCode start code
@throws IOException exception
hbase-backup/src/main/java/org/apache/hadoop/hbase/backup/impl/BackupManager.java