The database system stores information about data changes in redo log entries in the log area (set of all log volumes). After a system failure, for example due to a hard disk error, you may need redo log entries from log backups to restore the database to the desired state. Therefore, regularly back up your redo log entries from the log area to data carriers.
Note that in the following case, you do not need backed-up redo log entries to restore the database after a system failure: If the database system could not write the latest data changes to the data area, but the log area was not damaged, you can restart your database, and the database system uses redo log entries from the log area to repeat the necessary data changes. More information: Example: Restart
If the log area is full, the database system cannot write any further redo log entries to the log area and stops all running transactions. This means that the database is unavailable for users. You can only continue working after you have backed up redo log entries from the log area to data carriers.
Exception: You have switched on the overwrite mode for the log area. This is not recommended in production systems though. More information: Glossary, Overwrite Mode for the Log Area
Note that you cannot start any other backup while a log backup is running. Exception: While the automatic log backup is active, you can carry out data backups.
You can only back up redo log entries after you have created at least one complete data backup of the database.
More information: Backing Up Data
You have defined a backup template.
More information: Backup Templates and Data Carriers
If you plan to back up to a data carrier on a remote computer (not the database computer), then additional preparations may be necessary.
More information: Backing Up and Restoring Data with Remote Computers
The database is in the ONLINE or ADMIN operational state.
For log backups, use Database Studio, Database Manager CLI, or CCMS (in SAP systems only).
Manual Log Backup
During a manual log backup, you back up all redo log entries that the system has written since the last log backup.
You can back up log entries to files or to pipes. When backing up to files, the system creates the necessary files one after the other. Each file has the size of a log segment. Note that restrictions apply for backing up to pipes, see Backup Templates and Data Carriers.
Activating or Deactivating Automatic Log Backup
If automatic log backup is on, the database system automatically backs up redo log entries to backup files.
The system starts a log backup at the following times:
When a log segment is full
You configure the size of the log segments with the general database parameter AutoLogBackupSize.
More information: General Database Parameters
When the configured time interval has elapsed
You can specify the time interval when switching automatic log backup on.
We recommend automatic log backup in particular for databases in which large amounts of data are changed and therefore a great number of redo log entries are written.
For automatic log backup, you cannot use pipes.
More information: SAP Note 869267
Archiving Backup Files
When you back up your log entries to files, you have to archive these backup files regularly.
More information: Archiving Backup Files