In RAC standby, only one standby instance performs the task of applying the redo logs to the database. This instance is known as the recovery instance and all other standby instances are known as receiving instances. When the recovery instance fails, the method of restarting the redo apply depends on whether the Data Guard Broker is configured. If the Broker is used, the redo apply restarts automatically on the first available standby instance. If the Broker is not used, the redo apply is restarted manually on one of the other standby instances.
Continentalclusters environment
A Continentalclusters configuration provides an alternative disaster recovery solution in which two clusters are geographically dispersed. For information about setting up Continentalclusters, see the document Designing Disaster Recovery HA Clusters Using Metrocluster and Continentalclusters Manual available at
A typical Continentalclusters environment consists of a primary cluster (SG Cluster 1) and a recovery cluster (SG Cluster 2). In the primary cluster, Data Guard is configured using the ODG toolkit while the Oracle database is placed on a disk that is shared between the nodes in the primary cluster. The standby database is created in the recovery cluster and is also placed on a shared disk. A recovery group is created in the Continentalclusters environment with the following three packages:
1.Primary package: This package is created on the primary cluster, using the ODG toolkit. It brings up the Oracle database on the primary cluster as a primary database and starts monitoring the primary database processes. If the primary database fails on Node 1, the primary package is failed over to another node within the Primary Cluster.
2.Data Receiver package: This package is created using the ODG toolkit on the recovery cluster. It brings the Oracle database on the recovery cluster in standby mode and starts monitoring the standby database processes. If the standby database fails, this package halts the Oracle database and fails over the package to another node within the recovery cluster.
3.Recovery package: This package is also created using the ODG toolkit on the recovery cluster. It is configured to bring up the Oracle database on the recovery cluster in the primary mode. Initially, this package is in a halted state. When the primary cluster fails, you must run the cmrecovercl command on the recovery cluster to bring up the recovery package.
NOTE: For a recovery package, the package attribute START_STANDBY_AS_PRIMARY is set to [yes].
Initially, the primary package and the Data Receiver package is up and running, and the recovery package is in a halted state. The primary package brings up the Oracle database on the primary cluster in primary mode and the Data Receiver package brings up the Oracle database on the recovery cluster in standby mode. Thus, a typical Data Guard environment is set up with data replication done from the primary database on the primary cluster to the standby database on the recovery cluster.
Multiple standby databases for the same primary database cannot be supported in a single Continentalclusters setup. This is because there can be only one Data Receiver package and only one recovery package in a given recovery group. However, the ODG toolkit in Continentalclusters does not restrict you from configuring other standby databases that are placed outside the Continentalclusters setup.
NOTE: The
Single Instance Environment
