Log Mode 

By setting the Log Mode you can decide how the log entries are backed up:

·         Simply (in older versions SINGLE)

·         Mirrored (in older versions DUAL)

For security reasons, we recommend that you always mirror the Log Area. This is either done with a hardware-based mirroring or using database software.

If your system provides hardware-based mirroring (RAID-1 systems), we recommend that you use this.

Mirrored Log Areas

The advantage of this configuration is that the system can continue operating even if one log area is temporarily out of action, and this log area can be reincorporated into the system while the system is running.

Simple Log Area

If you are using hardware-based RAID-5 or RAID-1 systems, you can use a simple log area, as these systems provide adequate operating backups for productive operation. Accesses to the log volume greatly influence the performance of the system as a whole. Therefore, watch out for a high data throughput when choosing a RAID system.

Only one log area is configured in this case. The log area should be backed up regularly.

If a disk error occurs, the content of the Log volume is lost and the data volume is therefore no longer consistent with the transaction. 

The database can be more or less fully restored by means of a complete Data Backup and, possibly, other Log Backups. Exceptions to this are any log entries that has not yet been backed up, and any open transactions.

See also:

Concepts, Logging