Syntax:
DROP LOGFILE GROUP logfile_group
    ENGINE [=] 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 [HELP CREATE LOGFILE GROUP].)

*Important*:

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
http://dev.mysql.com/doc/refman/5.5/en/mysql-cluster-disk-data.html.

URL: http://dev.mysql.com/doc/refman/5.5/en/drop-logfile-group.html

