Changing the Log Mode from DUAL to SINGLE 
Use
You can change the
log mode for the current
database instance.
Prerequisites
There are no open parameter sessions (
Closing a Parameter Session).The database instance can be in any
operational state.
The current log mode is DUAL.
Procedure
Under New LogMode, select the option SINGLE.
To change the log mode in the parameter file of the database instance, you must restart the database instance. If you are not in the OFFLINE operational state, select the option
Restart Database implicitly after LogMode change.
Confirm your entries.
Choose LogMode ® Change LogMode.
Result
The new log mode SINGLE is displayed as the current log mode.