It is permissible to drop redo log files so that a multiplexed redo log becomes temporary asymmetric. However, you should rectify this situation immediately so that all groups have at least two members.
I’d like to try to drop one of the member that i have just created for demo. The following error message displayed:
SQL> alter database drop logfile member '/u01/oradata/kysnail/redo
04a .log';
alter database drop logfile member '/u01/oradata/kysnail/redo04a .log'
*
ERROR at line 1:
ORA-01609: log 4 is the current log for thread 1 - cannot drop members
ORA-00312: online log 4 thread 1: '/u01/oradata/kysnail/redo04.log'
ORA-00312: online log 4 thread 1: '/u01/oradata/kysnail/redo04a .log'