Chapter 1 Introduction To Red Hat Cluster Manager; Cluster Overview; Disk Storage - Red Hat CLUSTER MANAGER - INSTALLATION AND Administration Manual

Section 1.1:Cluster Overview
1 Introduction to Red Hat Cluster
Manager
The Red Hat Cluster Manager is a collection of technologies working together to provide data in-
tegrity and the ability to maintain application availability in the event of a failure. Using redundant
hardware, shared disk storage, power management, and robust cluster communication and application
failover mechanisms, a cluster can meet the needs of the enterprise market.
Specially suited for database applications, network file servers, and World Wide Web (Web) servers
with dynamic content, a cluster can also be used in conjunction with the Piranha load balancing cluster
software, based on the Linux Virtual Server (LVS) project, to deploy a highly available e-commerce
site that has complete data integrity and application availability, in addition to load balancing capabil-
ities. See Section B.5, Using Red Hat Cluster Manager with Piranha for more information.

1.1 Cluster Overview

To set up a cluster, an administrator must connect the cluster systems (often referred to as member
systems) to the cluster hardware, and configure the systems into the cluster environment. The foun-
dation of a cluster is an advanced host membership algorithm. This algorithm ensures that the cluster
maintains complete data integrity at all times by using the following methods of inter-node commu-
nication:
• Quorum partitions on shared disk storage to hold system status
• Ethernet and serial connections between the cluster systems for heartbeat channels
To make an application and data highly available in a cluster, the administrator must configure a clus-
ter service — a discrete group of service properties and resources, such as an application and shared
disk storage. A service can be assigned an IP address to provide transparent client access to the ser-
vice. For example, an administrator can set up a cluster service that provides clients with access to
highly-available database application data.
Both cluster systems can run any service and access the service data on shared disk storage. However,
each service can run on only one cluster system at a time, in order to maintain data integrity. Adminis-
trators can set up an active-active configuration in which both cluster systems run different services,
or a hot-standby configuration in which a primary cluster system runs all the services, and a backup
cluster system takes over only if the primary system fails.
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