Continuous or Manual Logical-Log Backup (ON-Bar) 
You can back up the logical log of the Informix database with
ON-Bar in continuous or manual mode:For continuous logical-log backup, you set the
The advantage of continuous logical-log backup is that the backup is performed when required, assuming that sufficient storage media is available. Therefore, you do not need to monitor the fill level of the logical log.

SAP recommends you to use continuous backup.
For manual logical-log backup, you set the
You must monitor your logical log and perform the logical-log backup manually before the log fills. Remember that a full logical log causes the database to stop processing.
For more information about setting the
ALARMPROGRAM and LOG_BACKUP_MODE parameters, see Setting Parameters for Logical-Log Backup (ON-Bar).
See also:
Informix documentation