About Archived Redo Log Files for an Oracle RAC Database

When you use Oracle Database Configuration Assistant (DBCA) to create your Oracle RAC database, each instance is configured with at least two redo log files that are stored in the shared storage area. If you have a two-node Oracle RAC database, then at least 4 redo logs are created for the database, two for each instance.

If you use a cluster file system to store the archived redo log files for your Oracle RAC database, then the redo log files are shared file system files. If you use ASM to store the archived redo log files for your Oracle RAC database, then each instance automatically has access to all the archived redo log files generated by the database. If you use shared storage or raw devices to store the archived redo log files on each node, then you must configure the operating system to grant access to those directories for each instance of the cluster database that needs access to them.

The primary consideration when configuring archiving is to ensure that all archived redo logs can be read from every node during recovery, and if possible during backups. During recovery, as long as the archived log destinations are visible from the node that performs the recovery, Oracle RAC can successfully recover the archived redo log data. For creating backups of your Oracle RAC database, the strategy that you choose depends on how you configure the archiving destinations for each node. Whether only one node or all nodes perform archived redo log backups, you need to ensure that the archived redo logs for every instance are backed up.

To backup the archived redo logs from a single node, that node needs to have access to the archived log files of the other instances. The archived redo log naming scheme that you use is important because when a node writes to a log with a specific filename on its file system, the file must be readable by any node that needs to access this archived redo log. For example, if node 1 archives a log to /oracle/arc_dest/log_1_100_23452345.arc, then node 2 can back up this archived redo log only if it can read/oracle/arc_dest/log_1_100_23452345.arc on its own file system.