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1. Where are the clusterware files stored on a RAC environment?

The clusterware is installed on each node (on an Oracle Home) and on the shared disks (the voting disks and the CSR file)

2. Where are the database software files stored on a RAC environment?

The base software is installed on each node of the cluster and the database storage on the shared disks. 

3. What kind of storage we can use for the shared clusterware files?

- OCFS (Release 1 or 2) 
- raw devices 
- third party cluster filesystem such as GPFS or Veritas 

4. What kind of storage we can use for the RAC database storage?

- OCFS (Release 1 or 2) 
- ASM 
- raw devices 
- third party cluster filesystem such as GPFS or Veritas

5. What is a CFS?

A cluster File System (CFS) is a file system that may be accessed (read and write) by all members in a cluster at the same time. This implies that all members of a cluster have the same view. 

6. What is an OCFS2?

The OCFS2 is the Oracle (version 2) Cluster File System which can be used for the Oracle Real Application Cluster. 

7. Which files can be placed on an Oracle Cluster File System?

- Oracle Software installation (Windows only)
- Oracle files (controlfiles, datafiles, redologs, files described by the bfile datatype)
- Shared configuration files (spfile)
- OCR and voting disk
- Files created by Oracle during runtime 

Note: There are some platform specific limitations. 

8. Do you know another Cluster Vendor?

HP Tru64 Unix, Veritas, Microsoft 

9. How is possible to install a RAC if we don’t have a CFS?

This is possible by using a raw device. 

10. What is a raw device?

A raw device is a disk drive that does not yet have a file system set up. Raw devices are used for Real Application Clusters since they enable the sharing of disks. 

More information about  this subject ( Oracle RAC Architecture ) you can get from  www.in-oracle.com

What is a Cluster ?
 

A cluster comprises of multiple interconnected servers or computers that appear as if they are one single server to end users and applications.

Oracle Database 10g Real Application Clusters (RAC) enables the clustering of the Oracle Database. A RAC database comprises of multiple instances residing on different computers to access a common database residing on shared storage.

The basic principle behind the Real Application Cluster is greater throughput and scalability due to the combined power of multiple instances running on multiple servers

Some of the main benefits of Oracle Real Application Cluster (RAC)


Scalability: Service capacity can be expanded simply by adding servers to existing cluster.
Availability round the clock (24/7): Zero downtime for database applications.
Relatively lower computing cost: Cost can be relatively reduced by using low-cost commodity hardware.
Grid Computing : Very foundation of Oracle Grid computing is oracle Real Application Cluster(RAC).

This information was taken from here.