Oracle 19c - Real Application Cluster(RAC) - RAC One Node - Overview - Part1

November 15, 2020  

Dear DBA Connections,

In this video, we are going to see the Oracle® Real Application Clusters (RAC) One Node feature in the Database Enterprise Edition, which was introduced with the 11g Release 2, provides enhanced high availability for single instance Oracle Databases, protecting them from both planned and unplanned downtime. The post also provides instructions for installing the Oracle Grid infrastructure, which is required to use One Node.

Introduction:

The One Node feature is a single instance of Oracle RAC running on one node of the cluster while the second node is in a cold standby mode. One Node allows customers to standardize their database deployment and management, consolidate database storage, and upgrade to a full multi-node Oracle RAC database without downtime or disruption.

With RAC, you can achieve continuous availability. There is little or no latency because transparent application failover (TAF), which is a failover routing mechanism, redirects transactions to a surviving server when a server crashes or a node becomes unavailable.

This is special because TAF performs quick clone of the instance to a new node. "If the node fails, Oracle Clusterware will automatically restart the Oracle RAC One Node instance on another server in the cluster."

TAF automates the instance relocation without any downtime and does not require manual intervention, which is a significant benefit. It uses Omotion, which facilitates instance migration or relocation.

RAC One Node versus RAC:

The main difference between Oracle RAC One Node and Oracle RAC is that with an Oracle RAC One Node Database, there is only one instance running at a time under normal operation. Should this one instance be impacted by unplanned downtime, there is a short period of time during which no database instance is running.

Traditionally, RAC is used in a multi-node architecture, with many separate instances residing on separate servers. RAC One Node is a multiple-instance of RAC running on a single node in a cluster and has a fast instance relocation feature in the event of a catastrophic or instant server failure.

RAC works as a live-live solution. The nodes in the cluster are all active and can accept connections and workloads and can work together as a single unit.

RAC One Node, as the name suggests as well, works as a live-standby solution, where only one node is active and the other nodes are available to accept the workload in case the active node goes down (planned or unplanned).

Benefits of RAC One Node:

The following list shows some benefits of the RAC One Node architecture:

• Sessions can be migrated from the active node while staying online.

• The online upgrade to RAC from RAC One Node (and vice-versa) is easy.

• Exadata is supported.

• Supported by using Oracle Virtualization Manager (OVM).

• Rolling Patches to RAC provide the same interface as RAC One Node.

• A One Node database using DBCA (from 11.2.0.2) can be created easily.

• One Node is supported on the same platforms as RAC.

• The cluster failover mechanism ensures high availability.

Prerequisites for Installation (on Oracle Linux 7.5)

Create a Virtual Machine and configure the following pre-requisites. After Installing and configuration done on first node, need to clone the VM for Second Node.

Before you install One Node, ensure that you perform the following tasks:

• As the root user, create the users and operating system (OS) groups that will own the Oracle software.

• Ensure that the date and time settings on all the nodes are set as closely as possible to the same date and time. You can use ntpd with the -x option or the Oracle Cluster Time Synchronization Service (CTSSD) to synchronize the time. Instructions on configuring ntpd with the -x option can be found in My Oracle Support ExtNote:551704.1.

• Configure Secure Shell (SSH) on each node in the cluster and ensure that you have the following rpms installed:

• Check the ASM libraries. Ensure that you have the following Oracle ASMLib downloads for Red Hat Enterprise Linux Server 7:

• Download the Grid and RDBMS installation software from the Oracle Downloads website. Choose the download binary depending on the platform on which you plan to install the software.

• Create a directory for the Oracle Grid CRS Home on both nodes.

High Level Steps:

Step1: Create a Virtual Machine with Installing Oracle Linux 7.5

Step2: Configuring Oracle Linux 7.5 for RAC Installation

Step3: Pre-requisites for RAC Installation

Step4: SSH Configuration and running runcluvfy

Step5: Clone a RAC installation configured VM for 2nd Node

Step6: Grid Infrastructure Installation

Step7: Database Binaries Installation

Step8: One Node RAC Database Creation

Cheers!

Ramesh.

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