Oracle RAC One Node

Oracle introduced a new option called RAC One Node starting from release Oracle 11g.
This option is available with Enterprise Edition only. It provide a cold failover solution for Oracle database.
It’s a single instance of Oracle RAC running on one node of the cluster while the second node is in a cold standby mode. If the instance fails then RAC One Node detects it and trie to restart the instance on the same node.
The instance is relocated to the second node in case there is a failure or fault in 1st node and the instance cannot be restarted on the same node.
Oracle uses Online Database Relocation using SVRCTL, which you can use to perform a live migration of database instances and connections to the other available cluster nodes
srvctl relocate database –d racxx –n nodeyy
You can add nodes that can be used for failover, but you cannot add additional instances without first converting Oracle RAC One Node to Oracle RAC.
You can convert from single instance to RAC One Node or RAC using Oracle Database Configuration Assistant (DBCA).
The benefit of this feature are:

    
• Rolling patches for single instance database

   

• Proactive migration / failover of the instance

    

• Live migration of instances across servers

    

• Online upgrade to RAC