My Intro:- Oracle RAC (Real Application Cluster)

Let say, your customer can not afford any downtime of the Data or Database in their organization, so that your customer definitely will ask you for the solution.

Are you searching for solution? The answer is High Availability!

Oracle Real Application Cluster is the perfect solution for High Availability and Scalability, where multiple instances (two or more instances) on different machines involved in RAC environment for single Database.

How is RAC different from non-RAC databases:- A non-RAC database has a single node while a RAC database has multiple(at least two) nodes. The nodes in a RAC, setup with shared storage. RAC offers failover option while a non-RAC database does not offer failover option because it is based on single node.

What are the other advantages of Oracle RAC environment in our organizations:-

Provide continuous availability Oracle RAC works as Maximum Availability Architecture, so that no need of downtime or no single point of failure.

Scale Oracle Database workloads For example, We can add or remove the Database instances within the Oracle RAC environment but minimum two instances or nodes is the requirement.

Oracle Cloud Database Services We can easily use Oracle RAC within Oracle Cloud Infrastructure (OCI). Oracle does not support Oracle RAC on Non-Oracle public cloud environments.

Database maintenance activity without downtime We can do different types of maintenance without downtime.

What do you mean is Cluster:- A cluster is a group of inter-connected computers or hosts or machines that work together to support applications and middleware (e.g. databases). 

What you think is Clusterware:- Clusterware is the software or the Program, which is responsible to run, manage and monitor the cluster to configure redundancy to prevent downtime and data loss. 

I prefer Oracle Real Application cluster software, but some of the popular searched Cluster software available and mentioned in below snap

What is Oracle Grid Infrastructure:- If you are planning to store your data in Oracle ASM, You need Grid Infrastructure software. This software is combination of two product (Oracle ASM and Oracle Restart) installed as the Oracle Grid Infrastructure home known as GRID_HOME.

What is Oracle ASM:- Oracle ASM (Automatic storage Management) is database file system and disk manager, introduced in Oracle 10g release to easily manage/configure/monitor and administration of the storage for database related files.

Who manages the ASM functionality:- Let say for example, If you checks the pmon process using the OS command, command:- ps-ef |grep pmon, You finds the output as +ASM This is ASM instance which is the responsible to control the functionality of ASM.

What is Oracle Restart:- Oracle Restart is the feature introduced in Oracle 11gR2 release, which controls the automatic restart of all the instances and services involved in Grid Infrastructure.

For example:- Let say, If the DB server or system rebooted or starts or restarts then DB instances are automatically starts with all the services.

Oracle Restart feature will automatically restart all database instances and services which have been registered with the Grid Infrastructure when the system is started.

Do you think any difference between Oracle RAC and Oracle GRID :- In simple words, Oracle RAC refers to Database where all the DB instances works together as a single entity. Oracle Grid is the software manages the cluster services such as ASM instances, cluster services etc.

Note:- You can refer or assume Oracle RAC is ORACLE_HOME and Oracle GRID is GRID_HOME

What is CRS (Cluster Ready service) :- Oracle clusterware is known as CRS (Cluster Ready Services) introduced in Oracle Database 10g.CRS is the main program that manages the high availability operations. The resource managed by CRS process is called CRS or Cluster resource, such as database, instance, service, listener, VIP address, or application process etc.

Are you aware of Oracle RAC one node:- This installation or setup or configuration also known as Active-Passive cluster, where all the Database services runs on only one node at a time and other node will be in a disabled or passive state.

Note:- In tis type of Oracle RAC, We need two Nodes or machines like Two node RAC.

Once failover happens, the other Node will be the Active node and all the DB services moved from first Node to Second Node and DB services runs on this Node.