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Posted Jan 26, 2011

Oracle Database 11g R2 RAC - The top 5 changes

By Karen Reliford

The introduction of the Oracle Grid Infrastructure product essentially combines Automatic Storage Management (ASM) and Oracle Clusterware into the same oracle home and product. With this new configuration, five main changes have been incorporated into Oracle Database 11g RAC. Read on to learn more.

With the release of Oracle Database 11g R2 a fundamental change was made that impacts a Real Application Cluster (RAC) based system. The cause of these changes is the introduction of the Oracle Grid Infrastructure product, which essentially combines Automatic Storage Management (ASM) and Oracle Clusterware into the same oracle home and product.

ASM was previously incorporated into the Oracle Database home and binaries, and Oracle Clusterware was a stand-alone product installed with its own home and binaries.

With this new configuration, five main changes have been incorporated into Oracle Database 11g RAC. These changes include installing and working with Grid Infrastructure, which includes setting up and configuring ASM; Single Client Access Names (SCAN), RAC One Node, Automatic Workload Balancing and the ASM Cluster File System (ACFS).

Single Client Access Name (SCAN)

SCAN simplifies the activities involved in adding and removing nodes from a RAC environment by configuring a single connection setting for all clients to use when connecting to a RAC database. Connections use EZconnect methodology to connect to the database regardless of which host machines the instances are currently running on.

For more information on Single Client Access Names you can view my article on SCAN by clicking here Single Client Access Name

RAC One Node

RAC One Node is a feature available with Oracle 11gR2 that essentially allows you to run a single instance database in a cluster and take advantage of the high availability and failover capabilities of Oracle RAC.

The database needs to be built as a "RAC" database, however, rather than selecting multiple nodes when running DBCA, the DBA would select to have only one node running one instance for the database.

If anything happens, the single instance can be migrated over to another node on the existing cluster. Even sessions can be automatically failed over to the new instance if Transparent Application Failover has been configured.

On Linux, a patch may need to be applied to the Oracle home prior to building the database. (RACONENODE_p9004119_112010_LINUX.zip). For more information on managing a RAC One Node Database, see Administering Oracle RAC One Node.

Oracle Grid Infrastructure

The Oracle Grid Infrastructure is a separate set of binaries from the Oracle Database software. It incorporates volume management functionality, file system functionality and the cluster management software. Essentially, Oracle Grid Infrastructure combines three products into one single Oracle Home. These three pieces are Oracle Clusterware, Automatic Storage Management (ASM) and the ASM Cluster File System (ACFS). In previous releases, Oracle Clusterware and ASM were installed into separate Oracle homes. ASM was included as part of the Oracle Database binaries, and Oracle Clusterware was a separate install. ACFS is new in Oracle 11g R2.

The Clusterware component of the Grid Infrastructure includes Cluster Management Services (known as Cluster Ready Services (CRS) in previous releases) and High Availability Services for both Oracle and other third party products. Installing Oracle Clusterware is a prerequisite activity for working with Oracle RAC.

Starting with Oracle 11g R2, ASM disks can be used for the clusterware files (OCR and voting disk). In previous releases, the OCR and Voting disk files had to be on raw partitions or a separate cluster file system.

ACFS is a general cluster file system that can be used for any type of data files.

The combination of these three components of the Oracle Grid Infrastructure now provides the primary foundation for Oracle 11g R2 RAC databases.

The six primary functions of Oracle Clusterware are Cluster Management, Node Monitoring, Event Services, Network Management, Time Synchronization and High Availability.

Cluster Management allows the cluster resources (such as databases, instances, listeners, services, etc.) to be monitored and managed from any node that is part of the defined cluster.

Node Monitoring is the "heartbeat" check of the nodes (and the resources running on them) to make sure they are available and functioning properly.

Event Services is the high availability messaging and response functionality for RAC.

Network Management involves managing the Virtual IP (VIP) addresses that are associated with the cluster and provides the consistent access to the RAC database regardless of the systems hosting it.

Time Synchronization is a new feature in Oracle 11g R2 that automatically synchronizes the timestamps of all of the nodes in the cluster. In previous releases, third party tools were generally used. Time Synchronization can be used in observer mode (if a Network Time Protocol is already in place) or active mode where one node is designated as the master node and all of the others are synchronized to it.

High Availability services monitor and restart any of the resources being managed by Oracle Clusterware.

For additional information about installing the Oracle Grid Infrastructure on Linux, see the Oracle Grid Infrastructure Installation Guide,

Automatic Workload Management (Policy Managed Databases)

In prior releases of Oracle RAC, the DBA would explicitly manage which nodes of a cluster would be used to run the various instances associated with a RAC database. Additionally, database services would be manually configured with preferred and available nodes, which facilitated the balancing of connections and failover of the services in a RAC environment.

In Oracle Database 11 g R2, a DBA can now configure a feature called policy-based management. This involves defining a server pool with the options of a minimum number of servers, a maximum number of servers and an importance level. The database itself would then be associated with a server pool rather than a specific set of nodes. This would allow Oracle to dynamically deliver services based on the total resources available to the cluster.

For example, if a cluster consisted of eight nodes in total and supported three RAC databases. Each database would be defined with a minimum and maximum number of servers. Let's assume that DB1 is defined with a minimum of 4 and a maximum of 6 with an importance of 10, DB2 is defined with a minimum of 2 and maximum of 3 and an importance of 7, and DB3 is set to a minimum of 2 and maximum of 3 with an importance of 5.

Initially the 8 nodes could be configured as nodes 1-4 allocated to DB1, nodes 5-6 allocated to DB2 and nodes 7-8 allocated to DB3. If node 3 failed for some reason, the system would allocate node 7 or 8 to DB1 because it has a higher importance than DB3 and a minimum requirement of 4 servers, even though it would cause DB3 to fall below the minimum number of servers. If node 3 is re-enabled it would be allocated immediately to DB3 to bring that database back to its minimum required servers.

If a 9th node were added to the cluster, it would be assigned to DB1 because of the importance factor and the fact that DB1 has not yet hit its maximum number of servers.

For more information on policy-managed databases, see the Oracle Real Application Clusters Administration and Deployment Guide.

ASM Cluster File System (ACFS)

ACFS is a multi platform cluster file system that has been designed to run on any platform that is supported by ASM rather than being specific to any one platform as some of the third party products are.

ACFS uses a file type called a dynamic volume, which can be used as a volume for a regular file system. The ASM Dynamic Volume Manager provides the interface between the dynamic volumes and the ACFS.

ACFS also provides a snapshot utility that does version enabling of the file system. These snapshots are online point-in-time copies of the ACFS. The storage for the snapshots is managed within ACFS and is very space efficient. Before any file is modified in ACFS, a copy is saved as a snapshot. The snapshot copies are designed to only capture the changed data. Snapshots can also be created on demand to provide consistent views of the ACFS system.

While ACFS can be used to store most files associated with Oracle, it must be noted that the Oracle Grid Infrastructure binaries themselves cannot be stored in ACFS. They must be installed locally on each node in the cluster.

All of the necessary services to manage ACFS systems are automatically managed by Oracle Clusterware. See the Oracle Automatic Storage Management Administrator's Guide for more information about ACFS.


Overall, since first releasing Real Application Clusters back with Oracle Database 9i it has been their premier high availability solution for databases. They have continued to add functionality and improvements over the Oracle releases since that date, and Oracle 11G R2 is no exception.

» See All Articles by Columnist Karen Reliford

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