ORACLE RAC ARCHITECTURE
The Oracle RAC environments have a one to many relationship between the database and instances.In other words, multiple instances access a single database.
Oracle RAC uses Oracle Clusterware for the infrastructure in order to bind multiple servers so that they operate as a single system.Oracle Clusterware also manages resources such as virtual Internet protocol, addresses,databases,listeners, services.
Oracle RAC is a unique technology that provides high availability and scalability for all application types.It prevents the server from being a single point of failure.Oracle Clusterware provides a complete integrated Clusterware management solution on all Oracle database platforms.
Oracle Clusterware functionality provides all of the features required to manage your cluster database,including Node membership, group services, global resource management and high availability functions.
Anything that Oracle Clusterware manages is known as a CRS, a cluster ready service resource.
A CRS resource can be a database, an instance, a service, a listener, a VIP address, or an application process.CRS resources are automatically started when the node starts and automatically restart if they fail.
An Oracle RAC database is a shared everything database, so all data files, control files, SP files and redo log files in Oracle RAC environments must reside on cluster aware shared disks so that all of the cluster database instances can access these storage components.All nodes in an Oracle RAC environment must also connect to at least one local area network or LAN,which is called a public network.
Oracle Clusterware hosts Node Virtual IP or IP addresses on the public network.Node VIPs are VIP addresses that clients use to connect to an Oracle RAC database.If a node fails, then the VIP address fails over to another node on which the VIP address can accept a TCP connection.So when the network on which the VIP is configured comes back online.Oracle Clusterware fails back the VIP to its home node So each instance has a buffer cache in its system.