Log Mode 

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

·        Simple backup

·        Mirrored backup

For the security of your data, we recommend that you mirror the Log Area. If your operating system allows hardware-based mirroring (RAID-1 systems), we advise you to use it.

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.

Single 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. For this reason, please ensure when you choose your RAID system that it has a high data throughput.

Only one log area is configured in this case. Back up this log area 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. You can still recover most of the content of the database instance using a full Data Backup,and, if necessary, further Log Backups. Exceptions to this are any log entries that has not yet been backed up, and any open transactions.

See also:

Database System Concepts, Logging Transactions