Step By Step Oracle 19C RAC Installation on Oracle Linux 7.9

Public IP:  The public IP address is for the server.  This is the same as any server IP address, a unique address with exists in /etc/hosts.

Private IP: Oracle RAC requires “private IP” addresses to manage the CRS, the clusterware heartbeat process and the cache fusion layer.

Virtual IP:  Oracle uses a Virtual IP (VIP) for database access.  The VIP must be on the same subnet as the public IP address.  The VIP is used for RAC failover (TAF). 

Networking Files:

The "/etc/sysconfig/network" file holds top-level networking configuration, including the hostname and gateway settings.

The "/etc/sysconfig/network-scripts/ifcfg-eth0" file holds the network configuration for the "eth0" adapter. If you have multiple network adapters, you would expect additional configuration files (eth1, eth2 etc.). The following example contains the configuration for a DHCP adapter.

The "/etc/hosts" file contains information for local name resolution.

The "/etc/resolv.conf" file is used to configure the location of the DNS servers to be used for name resolution. There can be multiple "nameserver" lines, one for each nameserver.

The "/etc/sysconfig/network-scripts" directory contains a number of network related scripts and commands. The ifdown and ifup commands are used to stop and start the specified network adapters.

The current network settings are displayed using the ifconfig command.

https://serhatcelik.wordpress.com/2021/02/15/step-by-step-oracle-19c-rac-installation-on-oracle-linux-7-9/

https://serhatcelik.wordpress.com/2021/02/18/step-by-step-oracle-19c-rac-installation-on-oracle-linux-7-9-part-2/

https://serhatcelik.wordpress.com/2021/02/20/step-by-step-oracle-19c-rac-installation-on-oracle-linux-7-9-part-3-database/

https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/networking_guide/sec-configuring_ip_networking_with_ifcg_files

https://oracle-base.com/articles/linux/linux-network-configuration#:~:text=The%20%22%2Fetc%2Fsysconfig%2Fnetwork%2Dscripts%2Fifcfg,configuration%20for%20a%20DHCP%20adapter.

How SID is different from Service name in Oracle:

 In short: SID = the unique name of your DB, ServiceName = the alias used when connecting.

SERVICE_NAMES specifies one or more names by which clients can connect to the instance. The instance registers its service names with the listener. When a client requests a service, the listener determines which instances offer the requested service and routes the client to the appropriate instance.

SID, DB Name, DB Domain, Global Database Name, Service Name, Service Alias and Instance Name in Oracle ?

SID = identifies the database instance (database name + instance number). So if your database name is somedb and your instance number is 3, then your SID is somedb3.

DB Name = Name of the database (database can be shared b/t multiple instances)

DB Domain = Usually the same as your company domain (somecompany.com)

Global Database Name = Database name + database domain (somedb.somecompany.com)

Service Name = A "connector" to one or more instances. It is often useful to create additional service names in a RAC environment since the service can be modified to use particular SIDs as primary or secondary connections, or to not use certain SIDs at all.

Service Alias = An alias to the service name (just like a CNAME, etc). Say you make your service name something meaningful to the dba, but perhaps it's a bit esoteric. Create a service alias and name it something that will be meaningful to the user.

Instance name = same as SID

Start up sequence:

The operating system starts ohasd (how):

Once the Operating system starts and finish the boot scrap process it reads /etc/init.d file via the initialisation daemon (INIT daemon >>) called init or init.d. The init tab file is the one it triggers oracle high availability service daemon

INIT daemon is very first daemon to be start  at the time of the operating system boot, we can say it  is system and service manager for the oracle linuxor any linux flavor. This services are start and stop through script which is stored in the /etc/init.d directory .

OHASD:-

Oracle High Availability Daemon   is the introduced in oracle 11g which is manage all clusterware resources , it is  responsible to start and monitor all local oracle clusterware daemon. We can say it is anchor for the all the process .

cat /etc/inittab|grep init.ohasd

h1:35:respawn:/etc/init.d/init.ohasd run >/dev/null 2>&1 </dev/null

HAS startup sequence:

– /etc/inittab

– /etc/init.d/init.ohasd

– /etc/rc.d/init.d/ohasd

– $GRID_HOME/bin/ohasd.bin

“/etc/init.d/init.ohasd” is started at runlevel 3 (networked, multi-user mode) or runlevel 5 (runlevel 3 + GUI).Logs present under “$GRID_HOME/log/<host_name>“.

/etc/inittab >>/etc/init.d/init.ohasd>>>/etc/rc.d>init.d/ohasd>>$GRID_HOME/ohasd.bin

“crsctl disable crs” updates a flag in “/etc/orale/scls_scr/<host_name>/root/ohasdstr“.

This file either contains “enable” or “disable” without any carriage return.

If “disable“, “/etc/rc.d/init.d/ohasd” will not startup.

nohup /etc/init.d/init.ohasd run &

 ohasd starts agents(whic all agent):

cssdagent - Agent responsible for spawning CSSD. >>> CSSD 

orarootagent - Agent responsible for managing all root owned ohasd resources.

         CRSD - Primary daemon responsible for managing cluster resources.

         CTSSD - Cluster Time Synchronization Services Daemon

         Diskmon

         ACFS (ASM Cluster File System) Drivers

oraagent - Agent responsible for managing all oracle owned ohasd resources.

         MDNSD - Used for DNS lookup

         GIPCD - Used for inter-process and inter-node communication

         GPNPD - Grid Plug & Play Profile Daemon

         EVMD - Event Monitor Daemon

         ASM - Resource for monitoring ASM instances  

cssdmonitor - Monitors CSSD and node health (along wth the cssdagent).

         CSSDmonitor

to start up daemons (gipcd, mdnsd, gpnpd, ctssd, ocssd,crsd, evmd asm etc), and 

crsd starts agents Which)

orarootagent - Agent responsible for managing all root owned crsd resources.

            Network resource - To monitor the public network

            SCAN VIP(s) - Single Client Access Name Virtual IPs

            Node VIPs - One per node

            ACFS Registery - For mounting ASM Cluster File System

            GNS VIP (optional) - VIP for GNS

oraagent - Agent responsible for managing all oracle owned crsd resources.

           ASM Resouce - ASM Instance(s) resource

           Diskgroup - Used for managing/monitoring ASM diskgroups.

           DB Resource - Used for monitoring and managing the DB and instances

           SCAN Listener - Listener for single client access name, listening on SCAN VIP

           Listener - Node listener listening on the Node VIP

           Services - Used for monitoring and managing services

           ONS - Oracle Notification Service

           eONS - Enhanced Oracle Notification Service

           GSD - For 9i backward compatibility

           GNS (optional) - Grid Naming Service - Performs name resolution

that start user resources (database, SCAN, listener etc).

http://rafik-dba.blogspot.com/2019/02/oracle-rac-startup-sequence.html

http://oracle-help.com/oracle-rac/rac-11gr2-clusterware-startup-sequence/