Oracle RAC DBA Resources

1. What is RAC?
Ans: Oracle Real Application Clusters (RAC) allow customers to run a single Oracle Database across multiple servers in order to maximize availability and enable horizontal scalability, while accessing shared storage.
In another words, Multiple Instances connecting / accessing a single Database is called RAC.

2. What is Grid Infrastructure?
Gird Infrastructure = Cluster + ASM
Cluster = Logical combinations of physical machines.
ASM (Automatic Storage Management) = ASM is used to store the data in shared mode.
Note:- Clusterware = It is a software to build the clusters.

3. What is the purpose of RAC?
Ans: Purpose of RAC is
   a. High Availability: If one instance go down other will be available for business users.
   b. Load Balancing: Means, user connections shared across all the instnaces.
   c. Failover: Means, When one instance is crashed, connections will be failover to available instances.
   d. Scalability: Means, we can add multiple instances if load on the data is more.

4. What are the different IP's used in RAC?
Ans: There are 4 IP's
   a. Public IP's: Used to connect to the servers (ex: by unsing putty tools).
   b. Private IP's: Used for cache fusion requests and cluster internal communications.
   c. Virtual IP's: Used for failover the connections.
   d. Scan IP's: Used for load balancing.

5. What are the services available in cluster?
Ans: In RAC, main services are :
   a. Oracle High Availability Service,
   b. Cluster Ready Service,
   c. Cluster Synchronization Service, and
   d. Event Manager Service.