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RAC Components

The Component Diagram (Fig. 4.1) shows a collection of all the components that inter-relate to each other and together make up the Oracle Real Application Cluster. This diagram will provide us a road map for discussion.

At a very high level, RAC architecture consists of these components:

  • Physical Nodes or Hosts

  • Physical Interconnects and interconnect protocols

  • Cluster Manager Software and Cluster Ready Services

  • Oracle Instances and Cache Fusion

  • Shared Disk System

  • Clustered File System, Raw Devices, Automatic Storage Management

  • Network Services

  • Workload Management Services – Virtual IP configuration

The overall structure of an Oracle Single-instance database is fairly complex. A complete Oracle instance consists of disk files, shared memory structures, and background processes. The shared memory area is further subdivided into numerous caches and pools that are used to transfer data, programs, and instructions from processes to and from the disks and users.

The Architecture of RAC

In this chapter, we’ll take a close look at the architecture of the RAC database system. RAC database is a multi-instance single database. We will examine all of the components that make up total architecture as well as discuss the inter-relations for these components.

RAC is the principal component for the Oracle Grid Architecture. Oracle’s Grid vision represents a pool of database servers, storage and networks into an inter-related resource platform. Effective Management of workload within the grid database computing arena is a key feature. RAC Database and clustering technology helps to set up and manage the overall Oracle Grid strategy. Database processing and capability can be easily and dynamically added with the RAC technology.

Let us keep in mind that Clusters and Grids have different vision and objectives. Clusters have static resources for a specific application. Grids, which can consist of multiple clusters and stand-alone servers, are dynamic resource pools and they are shareable among many different applications and users. A grid does not assume that all servers in the grid are running the same set of applications.   

RAC Components

Each of the instances in the cluster configuration communicates with other instances by using the cluster manager or clusterware. Clusterware is the middleware that glues all the clustered instances and projects in a single database system image.

Cluster platforms depend on the cluster management program to track the cluster node status (whether or not nodes in the cluster are available for work). Essentially, there are two types of cluster managers, vendor supplied and Oracle supplied.

HP supplies TruUnix TruCluster and HP-UX MC/Service Guard), IBM supplies HACMP/ESCRM for AIX platform and several other platforms that the vendor will supply the cluster manager. RAC is also certified for use on Sun Solaris using Sun Cluster version 3.0, Veritas DBE/AC version 3.5, and Fujitsu-Siemens Prime Cluster versions 4.1, and 4.0. RAC is also available for HP Alpha OpenVMS (VMS is cluster aware out-of-the-box so no clusterware is needed). For Linux and Windows, Oracle provides the cluster management software. To implement Oracle RAC on IBM-OS/390, you need to have the XCF clusterware that is compatible with your release of OS/390.

Clusterware, regardless of who supplies it, provides node monitoring for the other nodes in your system. By means of a "heartbeat" signal sent over the cluster interconnect; all nodes in a RAC cluster keep track of what nodes are available, which ones are unavailable, and whether or not a node becomes available.

With 10g release, Oracle provides portable clusterware, which works on all the platforms to implement RAC database solution. Oracle provided clusterware can be used independently or on top of the vendor provided cluster software. In case of Windows and Linux platform, the Oracle provided clusterware is the only choice.  In other platforms such as Solaris, HP-UX and TruUnix; you have choice of the vendor supplied cluster software. Oracle provided portable clusterware is named and packaged under the title ‘Cluster Ready Service’ (CRS). In fact, CRS is much more than the cluster software. It provides a method to configure High Availability (HA) services and Oracle Notification Services (ONS). We will examine more details on the CRS in later part of this chapter.

RAC Components

The shared storage provides the concurrent access by all the cluster nodes to the storage array. The storage array is presented in the form of LUNS (logical units) to the cluster host or node, and the file system is mounted on all the nodes. Thus, when the same file system is mounted and used on all the nodes in the cluster, it is called cluster file system. There are many flavors of approved cluster file systems such as HP’s CFS, Veritas CFS, PolyServe CFS and Oracle CFS (OCFS). At the same time, you still have the option to use the raw devices for many of the RAC database requirements.

With 10g release, Oracle provides a very flexible and high performing shared storage methodology, which is known as “Automatic Storage Management” (ASM). The method of ASM can be used in lieu of the cluster file system.


Figure 4.1 All the Logical and Physical Components of RAC

The above text is an excerpt from:

Oracle 10g Grid & Real Application Clusters
Oracle 10g Grid Computing with RAC
ISBN 0-9744355-4-6

by Mike Ault, Madhu Tumma


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