Steps Need to be followed for installation.

Server Node requirement  . 


1) A minimum of 2 GB RAM is required for the complete Grid Infrastructure and RAC software installation

2) Configure the server swap size to be 1.5 time if the RAM on the server is <=2 GB. Otherwise, configure the sever swap size to be equal to the RAM size


2) A minimum of 1 GB free space is required in the /tmp directory.


3) A minimum of 10 GB free space is required for the entire Clusterware home , Grid home  and RAC software home .


4) shared storage space to place Clusterware critical components like Oracle Cluster Registry (OCR) and Voting Disk.


5)  shared storage disks for Automatic Storage Management, if you consider using ASM to host the datafiles



6) Network requirements are .

every node that is going to be part of the cluster must be configured with a minimum of two NIC interfaces 
one for the public communication and another for the private communication.
You also need to secure three IP addresses, Public, Private, and VIP respectively for each individual node.
The VIP subnet must be configured on the same subnet as the public address



3) configure Kernel parameter using /etc/sysctl.conf file
4) Install RPM packages.
5) create Groups and users.
6) Set or configure limits for the user in order to improve the shell limits using /etc/security/limits.conf file

7) Add session user limits
/etc/pam.d/login
8) set the .bash_profile
if [ $USER = "oracle" ]; then
              if [ $SHELL = "/bin/ksh" ]; then
                 ulimit -p 16384
                 ulimit -n 65536
           else
              ulimit -u 16384 -n 65536
           fi
              umask 022
   fi 
9) configure the Secure Shell (SSH) passwordless connectivity between the nodes.

(This can be configured in 2 ways.
a) manually it was untill 11.1 release
b) it's been automated in 11.2 release . It can be configured automatically by OUI during installation phase.
The preceding configuration prerequisites are best done with the coordination of storage, system, and network teams.)

10)Verifying prerequisites with the CLUVFY utility 

we can further ensure that everything is in the right place just before the installation process kicks off. With the CLUVFY utility . Cluster Verify utility

Where do you get this cluster verify utility(runcluvfy.sh) ? 
Clusterware software location or grid software location.

How do you check node accessibility between nodes using Cluster verify utility.?
runcluvfy.sh : Run cluster verify utlity
./runcluvfy.sh comp nodereach –n raclinux1,raclinux2 –verbose
                                
This command will work in all rac release.



How to check if node accessibility, user equivalence, network interface, and shared storage are configured properly or not?
./runcluvfy.sh stage -post hwos -n raclinux1,raclinux2 –verbose . This command is availabe from 11g r2

cluvfy stage -post hwos -n node_list [-s storageID_list] [-verbose]

Use the cluvfy stage -pre crsinstcommand with either the -file, -n, -flex, or -upgrade parameters to check the specified nodes before installing or upgrading Oracle Clusterware.

Use the cluvfy stage -post crsinstcommand to check the specified nodes after installing Oracle Clusterware.

One more command is there to check
./runcluvfy.sh stage -pre crsinst -n raclinux1,raclinux2 –verbose

What is Fixup flag ?
when the –fixup flag is used with the CLUVFY utility, it creates the fixup shell script in the directory named with the fixupdir flag for those requirements that have failed to meet the prerequisites criteria on the servers
You can, as the root user, execute those scripts over the servers to fix the problems reported during the checks validation. 
./runcluvfy.sh stage -pre crsinst -n raclinux1,raclinux2 –fixup –fixupdir /tmp/fixups.sh

(Initiating Oracle Universal Installer for Oracle 11g R1 Clusterware
===================================================================
How many installation procedure in RAC

Unlike the standalone installation process, Oracle Real Application Clusters (RAC) comes in a two-phase installation procedure; an Oracle Clusterware is configured in the first phase, followed by the Oracle RAC (RDBMS) software installation process


2 Phase
=======
1) Oracle Clusterware installation
2) Oracle RAC database installation.)

(How do you start clustware configuration ?)
To begin the Clusterware configuration proceedings,initiate the ./runInstaller command from the Oracle 11g R1 Clusterware staging area

(Explain all steps of Clusterware configuration)
1) Welcome Screen appears
2) OUI(Oracle universal installer) will inform you to enter ORacle inventory directory and Operation system group name.
If Oracle_Base is already set then , then Oracle by default suggest appropriate location.
3) Enter Oracle Clusterware home name and specify oracle clusterware location for Oracle Clusterware software binaries.
4) (Product specific Prerequisite check)after this , OUI then performs mandatory prerequisite checks to ensure that all essential recommendations such as kernel parameters value, physical memory, OS packages, and settings are actually met on nodes. 

5)next OUI will display Cluster Configuration like (: in which the OUI detects and displays the) local node's Public, Private, and VIP name details under the Cluster Name section, as configured in DNS or as mentioned in the /etc/hosts file.
 ( In order to add more node details that are likely to be part of the Clusterware installation, click on the Add button and enter the Public, Private, and VIP names for each node.)

  The Cluster Name field suggests a default cluster name for this cluster environment.( As a best practice, ensure you set a unique cluster name if you are going to hold multiple cluster environments in your network.) It can be modified as per the environment. 

6)Specify Network Interface Usage ,( you are required to configure the network interface types for the public and the private communication. )
Here , By default, the public and private interfaces are configured to private interface type. However, do not worry; select the correct interface from the list for the public interface.

7)Specify Oracle Cluster Registry (OCR) Location  and enable redundancy level:( OCR is one of the critical components of an Oracle Clusterware, which maintains and manages essential details for the cluster sources s
Such as RAC databases, listeners, instances, and services. As of Oracle 11g R1, OCR can be placed either on a shared block on a raw device or on a shared filesystem to which all the participating nodes must have read and write permissions)


(Considering the criticality of the OCR contents to the cluster functionality, 
Oracle provides an option to make (mirror) the OCR file redundant, with a Minimum of two copies, to avoid a Single Point of Failure situation.
 To enable the Oracle redundancy option, choose the Normal Redundancy option and specify the mirror copy disk location accordingly
If you are depending on the system-provided (RAID) protection level, you can then choose the External Redundancy option.
 However, Oracle strongly recommends you to multiplex the OCR file. )

(Next you need to provide path of the OCR.)
8) Specify Voting Disk location and redundancy level (configuration ): (The voting disk is another critical constituent of an Oracle Clusterware, which maintains and consists of important details about the cluster nodes membership, such as which node is part of the cluster, who (node) is joining the cluster, and who (node) is leaving the cluster.

Given the importance of voting disk availability, Oracle provides Normal and External redundancy options to multiplex the voting disk to maintain high availability)

(You will need to ensure that all the nodes participating in the cluster have read/write permissions on disks.
Specify voting disk location and you can have upto max 32 voting disk in a cluster.

Not Understood : Note: A node in the cluster must be able to access more than half of the voting disks at any time in order to be able to tolerate a failure of n voting disks. Therefore, it is strongly recommended that you configure an odd number of voting disks such as 3, 5, and so on.)

9) Install ,Once the installation begins on the local node, OUI displays the progress installation bar


10)Once installation is done , OUI then brings up a pop-up Execute Configuration scripts window
log in as root user, and you must run the scripts (orainstRoot.sh and root.sh) in sequence across all the nodes as instructed.

11).When the root.sh script is executed successfully across the nodes, click on OK to complete the Oracle Clusterware Installation process and proceed to the final stage.

12)Configuration Assistants, OUI then moves further to configure Oracle Notification, Private Interconnect, and Cluster Verifications Utility (CLUVFY) on the Configuration Assistants screen