All of the nodes in a RAC should have the same tnsnames.ora entry,
let us say you have 2 node oracle cluster, login to each node and
issue tnsping for the SID name that you want to check, i.e., tnsping
myprd1 the result should come out as OK, once this check is performed
you are all set to create the dblink:-

CREATE PUBLIC DATABASE LINK myprddblink
CONNECT TO devuser IDENTIFIED BY devpwd
USING myprd1;

Select count(*) from table@myprddblink;

If for some reason you get the famous tns names error then
make sure you have the SID name configured correctly in the
tnsnames.ora file.

Include the following information:

* Your cluster hardware specifications, for example, a two-node cluster of Dell PowerEdge 6100 servers
* Your operating system version
* All five digits of the release number of your Oracle RDBMS (for example, 9.2.0.0.1)
* All five digits in the release number of your Oracle9i Real Application Clusters database
* On Windows NT and Windows 2000, the contents of HKEY_LOCAL_MACHINE\SOFTWARE\ORACLE\OSD key
* Cluster OSD upgrades from vendor
* Information about the particular operation that failed, for example, database startup or query
* A list of steps that reproduce the problem

Changing the Archiving Mode in Real Application Clusters

After configuring your Real Application Clusters environment for RMAN, you can alter the archiving mode if needed. For example, if your Real Application Clusters database uses NOARCHIVELOG mode, then follow these steps to change the archiving mode to ARCHIVELOG mode:

1. Shut down all instances.
2. Reset the CLUSTER_DATABASE parameter to false on one instance. If you are using the server parameter file, then make a sid-specific entry for this.
3. Add settings in the parameter file for the LOG_ARCHIVE_DEST_n, LOG_ARCHIVE_FORMAT, and LOG_ARCHIVE_START parameters. You can multiplex the destination to use up to ten locations. The LOG_ARCHIVE_FORMAT parameter should contain the %t parameter to include the thread number in the archived log file name. You must configure an archiving scheme before setting these parameter values.
4. Start the instance on which you have set CLUSTER_DATABASE to false.
5. Run the following statement in SQL*Plus:

SQL>ALTER DATABASE ARCHIVELOG;

6. Shut down the instance.
7. Change the value of the CLUSTER_DATABASE parameter to true.
8. Restart your instances.

You can also change the archiving mode from ARCHIVELOG to NOARCHIVELOG. To disable archiving, follow the preceding steps with the following changes:

1. Delete the archiving settings that you created in step 3.
2. Specify the NOARCHIVELOG keyword in step 5:

ALTER DATABASE NOARCHIVELOG;

Starting the Console To use the Oracle Enterprise Manager Console, start the following components:

1. An Oracle Intelligent Agent on each node
agentctl start
2. A Global Services Daemon (GSD) on each node
gsdctl
3. The Management Server
4. The Oracle Enterprise Manager Console

gsdctl is used to start and stop the gsd ctl. Following are the options available for gsdctl:-

You can use gsdctl commands to start, stop, and obtain the status of the GSD service on any platform. The options for gsdctl are:
* gsdctl start — To start the GSD service
* gsdctl stop — To stop the GSD service
* gsdctl stat — To obtain the status of the GSD service

Start the GSD on both nodes by logging in and issuing the commands below:-

$gsdctl start

Starting a configured RAC database is no different from starting a single node database, the only additional component to start is gsd. Gsd is global services daemon which is used for other Oracle components such as SRVCTL, DBCA and Enterprise manager.

Start the listener on each node.

$lsnrctl start

Connect to Node 1 and issue the following commands through sqlplus GSD writes to the following directory:- $ORACLE_HOME/srvm/log

$sqlplus /nolog
SQL>connect / as sysdba
SQL>startup

Connect to Node 2 and issue the following commands through sqlplus

$sqlplus /nolog
SQL>connect / as sysdba
SQL>startup

Now both nodes are started. Veryify that both nodes are running by issuing the following command:-

SELECT * FROM V$ACTIVE_INSTANCES;