It is very important to archive the offline redo log files, because these are essential if you have to recover the database.
The following graphic shows a typical archiving scenario with RAC:
Offline redo log files of different instances can be stored in the common archiving directory located on a shared file system of another instance. This can occur if the online redo log files of a particular instance have not been saved in the archiving directory for a long time.
Possible reasons are that the instance is closed or it is started but not active. Therefore, since a redo log file change is not forced, Oracle archiving is not activated. One of the “active” instances notices this status and makes sure that the current online redo log file of the affected instance is saved in the archiving directory.
Therefore, you must set the parallel_instances parameter in the init<DBSID>.sap profiles used by BRARCHIVE, so that BRARCHIVE can find and archive the offline redo log files of the other Oracle instances.
· There is only one volume pool managed by BRARCHIVE.
· The entire BRARCHIVE functionality is available, even continuous archiving with the option -f.
· Only the disk space in the global archiving directory must be provided.
· Normally there is a global archiving directory created in the cluster file system. This directory can be accessed from every node of the RAC system. All the archiving processes save the online redo log files to the global directory in this way.
Definition of the global archiving directory in spfile:
log_archive_dest = /oracle/RAC/oraarch/RACarch
log_archive_format = %t_%s.dbf
· %t – Thread number (for identifying the instance)
· %s – Log sequence number
The Oracle placeholder @ (for ORACLE_SID) must not appear in the name of an offline redo log file. This means that it must not appear in either log_archive_dest nor in log_archive_format.
You start BRARCHIVE only on the host of one Oracle instance, generally on the dedicated database (DDB) instance. It archives all offline redo log files of all the Oracle instances.
BRARCHIVE creates a separate summary log, arch<DBSID>.log, for every Oracle instance. These logs are stored in the global saparch directory.