In an Oracle Real Application Clusters (Oracle RAC) environment, database files are stored and managed across multiple cluster nodes. Every instance can access the data files, including the data files associated with Undo tablespaces and control files. Each Instance has an Undo Tablespace dedicated to it that is stored on the shared storage. All redo log files are accessible to all instances, each redo log file is multiplexed as in a single instance. When using Oracle ASM with normal redundancy each redo log member is mirrored, and a second Multiplexed member is placed in a different disk group. Each instance has at least two redo log groups also called a thread. The Oracle RAC database files include:
- Data Files: These files contain the actual data, such as tables and indexes. In an Oracle RAC deployment, data files are stored in a shared storage that is accessible to all cluster nodes.
- Control Files: These files are essential for the database operation. They contain metadata about the database, such as database name, checkpoint information, and log sequence numbers.
- Redo Log Files: These files record all changes made to the database. In an Oracle RAC environment, redo log files are shared among all instances to maintain data consistency and facilitate instance recovery.
- Archive Log Files: These files contain a record of all changes made to the database, which are necessary for recovery operations such as database point-in-time recovery. Similar to redo log files, archive log files are shared among all Oracle RAC instances.
- Parameter File: These files contain initialization parameters that are used to configure the database instance. In Oracle RAC, a common approach is to use a shared SPFILE stored on shared storage to ensure consistency across all instances.
- Backup Files: These files, including data backups, control file backups, and archived redo log backups, are also stored on a shared storage that is accessible to all nodes for disaster recovery and restore operations..
A common (default) SPFILE with both the common parameters and instance specific parameters is highly recommended in shared storage. The SPFILE can be stored in Oracle ASM. Some initialization parameters are the same across all instances in a cluster, and some are unique per instance.
In an Oracle RAC environment, while most files like data files, control files, and generally redo log files are shared across all instances to ensure consistency and availability, certain files can be local to each instance. These include local temporary files, trace files, instance-specific redo logs, dump files, and optionally password files. The Database Password file (orapwd*) may be placed in shared storage, or may be on each local node. This file contains the passwords of privileged user and must be available when the database in NOT open.