MySQL 5.7 Reference Manual Including MySQL NDB Cluster 7.5 and NDB Cluster 7.6
DROP LOGFILE GROUPlogfile_groupENGINE [=]engine_name
      This statement drops the log file group named
      logfile_group. The log file group must
      already exist or an error results. (For information on creating
      log file groups, see Section 13.1.15, “CREATE LOGFILE GROUP Statement”.)
    
        Before dropping a log file group, you must drop all tablespaces
        that use that log file group for UNDO
        logging.
      
      The required ENGINE clause provides the name of
      the storage engine used by the log file group to be dropped.
      Currently, the only permitted values for
      engine_name are
      NDB and
      NDBCLUSTER.
    
      DROP LOGFILE GROUP is useful only
      with Disk Data storage for NDB Cluster. See
      Section 21.6.11, “NDB Cluster Disk Data Tables”.