RAC One Node databases are RAC databases that run in a cluster, but usually just run one instance. This single instance of Oracle RAC runs on one node in a cluster. With Oracle RAC One Node, you can standardize all Oracle Database deployments across the enterprise. You can consolidate many databases into a single cluster with minimal overhead, while providing the high availability benefits of fail-over protection, online rolling patch application, as well as rolling upgrades for the operating system and Oracle Clusterware.
The online database relocation utility is provided to migrate an Oracle RAC One Node instance to another node in the cluster without downtime to the application. Online database relocation starts a second instance on another node, shuts down the original instance, which disconnects sessions as they finish their transactions, then migrates the sessions to the new node. After the instance has been migrated, you can patch or upgrade the node. After you have completed maintenance, you can then migrate the Oracle RAC One Node back to its original home.
Oracle Clusterware provides fail-over protection to Oracle RAC One Node. If the node fails, Oracle Clusterware automatically restarts the Oracle RAC One Node instance on another server in the cluster.
You use the Database Configuration Assistant (DBCA) to create this type of database. After you start the DBCA, the Welcome page enables you to select Oracle RAC One Node as the database type you want to create.
A RAC One Node database can be administrator-managed or policy-managed. An administrator-managed RAC One Node database needs specific candidate servers configured for fail-over. A policy-managed RAC One Node database selects a fail-over candidate server from the associated server pool. Step 3 in DBCA, "Database Identification," enables you to select one of these choices.
To determine whether a database is a RAC One Node database, click the View All Properties link in the General section of the Cluster Database Home page. If it is a RAC One Node database, the Database Type entry at the bottom of the Properties page will have a label of RAC One Node.
RAC One Node databases are administered slightly differently from RAC or Single Instance databases.
You need to manage the candidate node list and ensure that a candidate node is always available for fail-over if possible.
You need to ensure that the server pools are configured so that a server is available for the database to fail over in case its node crashes.
An online database relocation operation cannot appropriate a server from a pool of lower importance; you must first move the server into the server pool and then initiate the online database relocation utility.
Oracle RAC One Node is supported on all platforms where Oracle Real Application Clusters (RAC) is certified.
Online Database Relocation Page
Enterprise Manager Information Roadmap
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