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B2BITS® Cluster Solution (CentOS Linux)

Page 4 of 20

November 13, 2008

Overview

Clustering uses specific hardware and software to join multiple systems together to function as a single

system and provide an automatic failover solution. If one of the clustered systems (also known as cluster

nodes, or nodes) fails, resources running on the failed system are moved (or failed over) to one or more

systems in the cluster by the RedHat Cluster Suite (RHCS) software. RHCS is the failover software

component in specific versions of the RedHat Enterprise Linux Server operating system.

Note: CentOS 5 Enterprise Linux is built on the Red Hat Enterprise Linux source code. Other than logo and name changes

CentOS Enterprise Linux is compatible with the equivalent Red Hat version.

When the failed system is repaired and brought back online, resources automatically transfer back (or

fail back) to the repaired system or remain on the failover system, depending on how RHCS is

configured.

Virtual Servers and Resource Groups

In a cluster environment, it is not a physical server that is being accessed; users access a virtual server,

which is managed by RHCS. Each virtual server has its own IP address, name, and hard drive(s) in the

shared storage system. RHCS manages the virtual server as a resource group, which contains the cluster

resources. Ownership of virtual servers and resource groups is transparent to users. See "Groups" section

of the appropriate document for more information on resource groups.

When RHCS detects a failed node or failed application, RHCS moves the entire resource group to

another node and remaps the virtual server to the new network connection. Users of an application ran on

the virtual server experience only a momentary delay in accessing resources, while RHCS re-establishes a

network connection to the virtual server and restarts the application.

Quorum Resource

A single disk, which is designated as the quorum resource, maintains the configuration data (including

all the changes that have been applied to a cluster database) necessary for recovery when a node fails.

The quorum resource can be any resource with the following attributes:

Enables a single node to gain and defend its physical control of the quorum resource

Provides physical storage that is accessible by any node in the cluster

Uses the Red Hat Global File System (GFS)

Shared Storage Systems

Cluster nodes can share access to external storage systems. However, only one of the nodes can own

any RAID volume in the external storage system at any time. RHCS controls which node has access to

each RAID volume in the shared storage system.

Cluster solution

Current cluster solution implements two-node clustering technology based on the RHCS software

incorporated within the CentOS 5 Enterprise Linux Server operating system. This cluster solution

provides the following benefits that meet the needs of mission-critical network application program

B2Bits FIXEdge server:

High availability of system services and resources to network clients

Redundant storage for application related data

Failure recovery for cluster-aware application

Flexible maintenance capabilities, allowing you to repair, maintain, or upgrade a cluster node

without taking the entire cluster offline

Each cluster node is configured with software, storage, and network resources that enable it to monitor

and interact with the other node to provide mutually redundant operation. If a cluster node fails for any

reason, virtual servers and resource groups are moved over to the healthy cluster node. When the failed

node is repaired and brought back to work, the virtual servers and resource groups are moved back to the

repaired node (if ordered so). In this manner, the cluster nodes operate as a single resource, rather than a

collection of individual systems. Because of the fact that the cluster nodes interact to assure their work,

virtual server appears as a single system to the network clients.

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