Prerequisites

1. Environment Planning

Before starting the installation, define the hardware and software specifications for the Oracle Real Application Clusters (RAC) environment.

Component	Specification
Operating System	Two CentOS 7.4 virtual machines
Disk Space	50 GB per node
Memory	4 GB per node
Network	Dual NICs recommended
Database Version	Oracle 19c
Shared Storage	ASM (Automatic Storage Management)

Ensure each virtual machine has two network interfaces and access to shared storage disks. The shared disks must be visible to both nodes.

2. IP Address Planning

Proper IP address planning is crucial for RAC functionality. The following IP types are required:

• Public IP: Used for client connections and management. Must be routable and configured before instalation.
• VIP (Virtual IP):strong> A floating IP that migrates to a surviving node during a failover. Not pingable until the cluster is installed.
• Private IP: Used for inter-node communication. Must be on a dedicated, private network.
• SCAN (Single Client Access Name): A single name used by clients to connect to the cluster. The SCAN listener resolves this name to one of the available RAC nodes.

Configure the /etc/hosts file on both nodes with the following entries. Ensure all IPs are on the same subnet.

# On node1 and node2
# Public IP
192.168.56.101 node1
192.168.56.102 node2
# VIP
192.168.56.103 node1-vip
192.168.56.104 node2-vip
# Private IP
10.0.0.1 node1-priv
10.0.0.2 node2-priv
# SCAN IP
192.168.56.105 rac-scan

3. Shared Storage Configuration

Oracle RAC requires shared storage accessible by all nodes. This is typically configured using a SAN or shared disks in a virtual environment.

In a VMware environment, attach at least two raw disks to each virtual machine. Ensure the disks are not independent and are shared between the nodes. After attaching, configure the shared bus setting in the VM's .vmx file:

scsi0.sharedBus = "virtual"
disk.locking = "FALSE"

4. ASM Disk Planning

Plan the ASM disk groups for different database components. A common setup includes separate disk groups for the Cluster Registry (OCR) and database data.

Disk Group	Purpose	Size
OCR	Stores cluster configuration information	3 GB
DATA	Stores database files	10 GB
ARCHIVE	Stores data base archive logs	5 GB

Installation Procedure

1. System Preparation

1.1 Install Dependencies

Install the necessary packages required by Oracle software using the package manager.

yum install -y binutils \
              compat-libcap1 \
              compat-libstdc++-33 \
              gcc \
              gcc-c++ \
              glibc \
              glibc-devel \
              ksh \
              libaio \
              libaio-devel \
              libgcc \
              libstdc++ \
              libstdc++-devel \
              libXi \
              libXtst \
              make \
              sysstat \
              elfutils-libelf-devel \
              unixODBC-devel

1.2 Create User and Groups

Create the required operating system groups and users for the Oracle Grid Infrastructure and Database software.

groupadd -g 501 oinstall
groupadd -g 502 dba
groupadd -g 503 oper
groupadd -g 504 asmadmin
groupadd -g 505 asmoper
groupadd -g 506 asmdba

useradd -u 600 -g oinstall -G dba,asmdba,oper oracle
useradd -u 601 -g oinstall -G dba,oper,asmadmin,asmoper,asmdba grid

passwd oracle
passwd grid

1.3 Create Directories and Set Permissions

Create the directory structure for the Oracle software and assign appropriate ownership and permissions.

mkdir -p /opt/oracle
chown -R grid:oinstall /opt/oracle
chmod -R 775 /opt/oracle

mkdir -p /opt/oracle/oraInventory
chown -R grid:oinstall /opt/oracle/oraInventory
chmod -R 775 /opt/oracle/oraInventory

mkdir -p /opt/oracle/grid
mkdir -p /opt/oracle/database
chown -R grid:oinstall /opt/oracle/grid
chown -R oracle:oinstall /opt/oracle/database
chmod -R 775 /opt/oracle/database
chmod -R 775 /opt/oracle/grid

1.4 Configure Kernel Parameters

Modify system limits and kernel parameters to meet Oracle requirements.

Edit /etc/security/limits.conf:

grid   soft   nofile    1024
grid   hard   nofile    65536
grid   soft   nproc     2047
grid   hard   nproc     16384
oracle soft   nofile    1024
oracle hard   nofile    65536
oracle soft   nproc     2047
oracle hard   nproc     16384

Edit /etc/pam.d/login and add the following line:

session    required     pam_limits.so

Edit /etc/sysctl.conf:

fs.file-max = 6815744
kernel.shmall = 2097152
kernel.shmmax = 536870912
kernel.shmmni = 4096
kernel.sem = 250 32000 100 128
net.ipv4.ip_local_port_range = 9000 65500
net.core.rmem_default = 262144
net.core.rmem_max = 4194304
net.core.wmem_default = 262144
net.core.wmem_max = 4194304

Apply the new kernel parameters:

sysctl -p

1.5 Time Synchronization

Disable the default NTP service and configure chronyd for time synchronization, which is preferred by Oracle.

systemctl stop ntpd
systemctl disable ntpd
mv /etc/ntp.conf /etc/ntp.conf.bak

systemctl enable chronyd
systemctl start chronyd

1.6 Security Settings

Disable SELinux and the firewall to prevent installation issues.

Edit /etc/selinux/config and set:

SELINUX=disabled

Reboot the system or run the following command to apply the change immediately:

setenforce 0

Permanently disable the firewall:

systemctl disable firewalld
systemctl stop firewalld

1.7 Set Environment Variables

Configure the environment variables for the oracle and grid users.

Edit /home/grid/.bash_profile:

export TMP=/tmp
export TMPDIR=$TMP
export ORACLE_SID=+ASM1
export ORACLE_BASE=/opt/oracle
export ORACLE_HOME=$ORACLE_BASE/grid
export PATH=$ORACLE_HOME/bin:$PATH
if [ $USER = "oracle" ] || [ $USER = "grid" ]; then
  if [ $SHELL = "/bin/ksh" ]; then
    ulimit -p 16384
    ulimit -n 65536
  else
    ulimit -u 16384 -n 65536
  fi
  umask 022
fi

Edit /home/oracle/.bash_profile:

export TMP=/tmp
export TMPDIR=$TMP
export ORACLE_BASE=/opt/oracle
export ORACLE_HOME=$ORACLE_BASE/database
export ORACLE_SID=rac1
export PATH=$ORACLE_HOME/bin:$PATH
if [ $USER = "oracle" ] || [ $USER = "grid" ]; then
  if [ $SHELL = "/bin/ksh" ]; then
    ulimit -p 16384
    ulimit -n 65536
  else
    ulimit -u 16384 -n 65536
  fi
  umask 022
fi

2. Cluster Configuration

2.1 Configure SSH Trust

Establish passwordless SSH connectivity between the oracle and grid users on all nodes to allow cluster software to communicate without manual intervention.

For the oracle user:

su - oracle
mkdir -p ~/.ssh
chmod 700 ~/.ssh
ssh-keygen -t rsa
ssh-keygen -t dsa
cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
cat ~/.ssh/id_dsa.pub >> ~/.ssh/authorized_keys

ssh-copy-id -i ~/.ssh/id_rsa.pub oracle@node2
ssh-copy-id -i ~/.ssh/id_dsa.pub oracle@node2

For the grid user:

su - grid
mkdir -p ~/.ssh
chmod 700 ~/.ssh
ssh-keygen -t rsa
ssh-keygen -t dsa
cat ~/.ssh/id_rsa.pub >> ~/.ssh/authorized_keys
cat ~/.ssh/id_dsa.pub >> ~/.ssh/authorized_keys

ssh-copy-id -i ~/.ssh/id_rsa.pub grid@node2
ssh-copy-id -i ~/.ssh/id_dsa.pub grid@node2

Verify the SSH connectivity:

ssh node2 date
ssh node2-priv date

2.2 Verify Package Installation

Confirm that all required packages are installed correctly.

rpm -q binutils \
       compat-libcap1 \
       compat-libstdc++-33 \
       gcc \
       gcc-c++ \
       glibc \
       glibc-devel \
       ksh \
       libaio \
       libaio-devel \
       libgcc \
       libstdc++ \
       libstdc++-devel \
       libXi \
       libXtst \
       make \
       sysstat \
       elfutils-libelf-devel \
       unixODBC-devel

2.3 Configure UDEV Rules for ASM Disks

Create UDEV rules to map raw disks to ASM-friendly device names. This ensures consistent naming across reboots.

Create a new file /etc/udev/rules.d/99-oracle-asm.rules:

# Rule for ASM disk /dev/sdb
ACTION=="add", KERNEL=="sd[b]", ATTR{size}=="*2048", RUN+="/bin/sh -c 'mknod /dev/asm-disk1 b %M %m; chown grid:asmadmin /dev/asm-disk1; chmod 660 /dev/asm-disk1'"

# Rule for ASM disk /dev/sdc
ACTION=="add", KERNEL=="sd[c]", ATTR{size}=="*2048", RUN+="/bin/sh -c 'mknod /dev/asm-disk2 b %M %m; chown grid:asmadmin /dev/asm-disk2; chmod 660 /dev/asm-disk2'"

Reload the UDEV rules and trigger device re-reading:

udevadm control --reload-rules
udevadm trigger --type=devices --action=change

2.5 Pre-Installation Checks

Use the Oracle Cluster Verification Utility (CVU) to perform a pre-installation check to identify any configuration issues.

$ORACLE_HOME/OPatch/opatch lsinventory
$ORACLE_HOME/runcluvfy.sh stage -pre crsinst -n "node1,node2" -verbose