Oracle RAC Basics

Oracle RAC is nothing but multiple nodes (each with an Oracle instance) access a same shared database.


 

  


Component of Oracle RAC

• Node
• Instance
• Database
• Clusterware software.
• Interconnect
• OCR and Vote disk

Node: Node is individual machine which has operating system install on it.

Instance: Instance is a way to access the database. It is combination of memory and background processes

Database: Database is set of Oracle files such as data file, Control files, Oracle redo log file and Archive log file

Clusterware software: It maintains integrity of Oracle database and manages shared and local resources.

Interconnect: Interconnect is nothing but network link between nodes. It maintains network heartbeat between RAC nodes. It also useful send block to other instance through network in case of cache fusion.

OCR: The OCR maintains cluster configuration information that is used by each node of the cluster to determine the state of the cluster. The OCR also maintains information on application resources that are defined within Clusterware such as databases, instance, services and the like and is therefore constantly changing. Each node in the cluster maintains a copy of the OCR in memory for better performance and each node is responsible for updating the OCR as required.

Vote Disk:The Voting Disk Files are used by Oracle Clusterware to determine which nodes are currently members of the cluster. The voting disk files are also used in concert with other Cluster components such as CRS to maintain the clusters integrity. As with most everything else Clusterware/RAC related, you need to consider redundancy in your architecture. Oracle expects that you will configure at least 3 voting disks for redundancy purposes. You should always configure an odd number of voting disks >= 3. This is because loss of more than half your voting disks will cause the entire cluster to fail.