The DBA�s Guide to Setting Up Oracle RAC One Node and Oracle Data Guard

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Oracle RAC One Node, a high availability option for Oracle Database 11g Release 2, is a hybrid of a classic active/passive cluster and the Oracle Real Application Clusters (RAC) option, the main difference with standard Oracle RAC being that an Oracle RAC One Node database will typically be active on one instance only. Oracle RAC One Node also allows the online migration of databases and their sessions for scheduled maintenance.

Oracle RAC One Node lowers the risk of unplanned outages as well. In case of a node failure, an Oracle RAC One instance will automatically be restarted on another candidate server. Furthermore, because the Oracle RAC One Node database is actually a cluster database, making the transition from Oracle RAC One Node to full-blown Oracle RAC is relatively straightforward.

Most businesses with a low Recovery Time Objective (RTO) rely on Oracle Data Guard, an Oracle Database Enterprise Edition feature, to restore service in the event of a severe failure or catastrophe. The initial lack of support of Data Guard for Oracle RAC One Node proved to be detrimental to the latter's adoption in many companies. But beginning with the 11.2.0.2 patch set released by Oracle in 2010, Oracle Data Guard can now be used to protect an Oracle RAC One Node database. (Oracle RAC One Node initially was available for a limited number of platforms only in the form of a one-off patch on top of the 11.2.0.1 base release, but it's now available on every supported platform for which the patch set has been released.)

In this article we will first explore the "broker" approach to an Oracle Data Guard setup, generally intended for less experienced DBAs or those who otherwise want less fine-grained control over the configuration. In Part 2, we will examine how to set up Oracle Data Guard with Oracle RAC One Node manually � the more advanced method. For simplicity, in both cases only one physical standby database is involved. (Basic understanding of Oracle Data Guard is assumed.)
The Setup

In the following sections we will assume that a primary Oracle RAC One Node database (named RON) has already been created and is up and running. In this example a four-node primary and an identical DR cluster are configured with Oracle 11.2.0.2 on Oracle Linux 5.5 64-bit. The databases are located in ASM, with db_create_file_dest set to disk group DATA, and a fast recovery area in disk group FRA.

The primary database RON is registered in the primary cluster's Oracle Cluster Registry with candidate servers node1 and node2 and domain example.com. A database service, RON_APP.example.com, has been created per Oracle's recommendation. (Note that user connections should always use this service instead of the ORACLE_SID to minimize problems during an online relocation.)

All diagnostic and administrative files are stored on an existing ACFS mount, called /data/oracle/RON/. This way the information is available across the cluster, a feature that greatly simplifies administration.

The below example shows the database configuration in the primary cluster's OCR:

$ srvctl config database -d RON
Database unique name: RON
Database name: RON
Oracle home: /u01/app/oracle/product/11.2.0.2/
Oracle user: oracle
Spfile: +DATA/RON/spfileRON.ora
Domain: example.com
Start options: open
Stop options: immediate
Database role: PRIMARY
Management policy: AUTOMATIC
Server pools: RON
Database instances:
Disk Groups: DATA,FRA
Mount point paths:
Services: RON_APP.example.com
Type: RACOneNode
Online relocation timeout: 30
Instance name prefix: RON
Candidate servers: node1,node2
Database is administrator managed

The DR database will be built on a different four-node cluster, with database nodes called drnode1 and drnode2. Note that it is not necessary to use four nodes; the majority of Oracle RAC One databases reside on two-node clusters.