From the database point of view:
online backups are by definition inconsistent backups because user changes are
written to files while backup is running and need some recovery from the archives
if you have to restore the backup. With the underlying RMAN tool you can even make
the time for restore really short.
why you ever would consider an offline backup of the database? Why have downtimes ?
While you can do an offline backup I don't see any advantage:
If you are in 24x7 you do online backups while the database is in archivelog mode , point.
The term Consistent means that when the backup completed everything was backed up and nothing new happened while the backup was going on ... its true in offline case..
online consistent backup -- its the backup where the database is not shutdown and the redo log files are generated while the backup is being taken.. so when the backup is complete there is a redo log switch and the brbackup takes the backup of only those redolog files that were generated during the backup... hence u can recover a database with it alone ... brarchive has no role in it as everything is done by brbackup. ( as Snowy mentioned )
Online backup is the backup without redo log files backup by brbackup .... there u have to use brarchive..
The only place which i think is the online consistent backup is used is whole database reset ..there too we can use offline backup.
Actually this condition is only for whole database reset ... we can recover the system with a unconsistent backup + the redo log backup ..
The Whole and Full backup have the difference when incremental backups and RMAN comes into picture....
Hope this is all what is there as far as backup is concerned...
Regarding SAP Database backups, we have different Backup types that could be used to backup the SAP database and restore the SAP system.
The basic methods used are SAP Offline and SAP Online backups.
SAP Offline Backup:
Here the SAP system is shutdown and the SAP tool for the database (BRTOOLS) is used for backing up the SAP database. During the backup only the SAP DataFiles with the control files are backed up into a specified directory of the server or a defined tape drive. The specifications are mentioned in the init<SID>.sap file. Since the SAP system is down during the backup process no changes are made to the SAP system or inturn the database from the SAP user point of view. Hence no logs are generated during this process. The offline backup of an SAP system is considered to be much consistent than an online backup.
SAP Online Backup:
The SAP system is un-disturbed during the backup procedure. The database is ready for editing during the backup process from the SAP user point of view. The changes done to the database through the SAP frontend is captured as logs during the SAP system online backup. The logs are stored as archive logs in the origlogA and origlogB directories. The backup process backups the SAP datafiles and at the end of this process backs up the archive logs that are generated during the process of the online backup.
The main difference in restoring a SAP system from an offline or a online backup as in offline backup only the datafiles that are backed up during the offline backup process are restored and the SAP system is activated. Whereas in a restore from an online backup restore after restoring the backed up datafiles the archive logs that were generated during the online backup process has to be applied for completing the restoration procedure.
For further details please refer the below given link,
Awarding points is highly appreciated.
Please incase you have further questions.