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Conversion of a Single Instance on a Cluster Running from a RAC-Disabled Oracle Home

Oracle RAC Cluster Tips by Burleson Consulting

This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters.  To get immediate access to the code depot of working RAC scripts, buy it directly from the publisher and save more than 30%.

On UNIX/Linux-based systems, where relink of the Oracle executables is possible, having a single instance running from a RAC-disabled Oracle home installation is possible, if improbable, if a one-node cluster with RAC installation was performed but later the RAC feature was disabled by unlinking it from the Oracle binary before creating the single instance database. An alternative method is to select the local, non-cluster option on the Node Selection screen in OUI to create a non-RAC-enabled single instance home on a cluster. The following technique can be used to convert this special type of single instance database into a RAC database:

1. On the cluster node where the single instance database is running, create a duplicate template of the database as described in previous sections using DBCA.

2. Change the working directory to the lib subdirectory in the rdbms directory under the Oracle home.

3. Relink the Oracle binary through use of the following commands:

make -f rac_on
make -f ioracle

At this point, the normal conversion procedure for a RAC enabled Oracle home can be used.

Conversion of a Single Instance on a Cluster Running from Non-Cluster Installed Oracle Home

This situation is only possible if the Local Installation option was specified on the OUI Specify Hardware Cluster Installation screen during an Oracle Database 10g installation.

To covert this type database to a RAC database, perform the procedures described under these previous sections:

* Duplicate the Original Single instance Database 

* Perform the Pre-Installation Steps

* Setting up the Cluster 

* Install Oracle Database 10g Software with RAC. In this step, make sure that a new Oracle home other than the one from which the single instance database was running is selected.

Required Post-Conversion Steps

After completing the conversion, the following items should be reviewed as covered in other chapters of this book:

* Use of load balancing and TAF

* Considering the use of locally managed tablespaces instead of dictionary managed tablespaces to reduce contention and manage sequences

* Properly configuring an interconnect for using automatic segment space management and for using SRVCTL to administer multiple instances

* Sizing of database buffer cache and shared pool: Database buffer cache and shared pool capacity requirements in RAC are greater than those in single instance Oracle databases. Therefore, increase the size of the buffer cache by at least 10% and the size of the shared pool by at least 15%.

* If ASM is used for the file systems, use RMAN for backup.

Moving HA Cluster to a RAC Cluster

Many enterprises currently have the High Availability (HA) clusters in their data centers. For example, a system may have a two node VCS based failover cluster. It is an Oracle single instance that is a part of one of the VCS Service groups. This section will briefly examine the issues and procedures involved in moving a HA based Oracle instance to multi-node RAC parallel database.

Procedure to Move the VCS to Veritas DBE/AC RAC

For this section, assume that there is a HA cluster, or so called Failover Cluster, supporting Oracle 9i Standalone Database. The single instance is implemented with VCS cluster framework. This is currently in an Active/Passive configuration.

To take advantage of the multi-node, scalable architecture of the parallel database, which is a 10g RAC, it must be migrated to the Oracle Database 10g RAC using the Veritas DBE/Advance Cluster software.

The following procedure can be used to undertake such migration.

A look at the current environment shows that there are two servers currently supporting a two-node HA cluster. All the Oracle Database Files are already on shared storage volumes. The database files are file system based files. Optionally, they may have been using the Quick I/O facility.


This is an excerpt from the bestselling book Oracle Grid & Real Application Clusters, Rampant TechPress, by Mike Ault and Madhu Tumma.

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.


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