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Object documentation Log Mode Locate the document in its SAP Library structure

You can use this log setting to control whether the log area is mirrored using software-based mirroring.

Note

By default, the database instance uses only one log area. Implement hardware-based mirroring using RAID-5 or RAID-1 systems to achieve a higher level of security for the database system. RAID systems guarantee a good level of security for production use of the database.

Mirroring the Log Area

If hardware-based mirroring is not possible, you can mirror the log area using database resources with the corresponding setting of the log mode.

In this case, the database instance uses the two log areas as follows:

·        Data is written to both log areas in parallel.

·        During a restart or log backup, the log entries are only read from one log area – the primary log entry.

·        When you use standard log backups, neither of the two log areas can be overwritten until the log entries of the primary log area have been backed up.

·        If access problems occur in the primary or secondary log area, the log volume in question is marked as BAD and the database instance is switched t the operational state OFFLINE.

·        The defective log volume of a log area can be restored in the operational state ADMIN. In this process, the complete contents of the relevant log volume are copied from the other log area to the defective log volume.

This ensures that the database instance does not have to be restored after a disk error that led to the loss of a log volume, as the content of the log volume was mirrored.

Procedure

Configure the required additional log volumes. Use the Database Manager to do this.
Database Manager GUI: SAP DB 7.4, section Changing Log Settings (Configuration Wizard)
Database Manager CLI:  SAP DB 7.4, section Changing Volume Parameters

 

 

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