13.1.1 How Sun Cluster works

The Sun Cluster system achieves high availability through a combination of hardware and software. The redundant cluster interconnects storage and public networks to protect against single points of failure. The cluster software continuously monitors the health of member nodes and prevents failing nodes from participating in the cluster, protecting against data corruption. Also, the cluster monitors services and their dependent system resources, and fails over or restarts services in case of failures. Sun Cluster supports up to 16 nodes (in Sun Cluster 3.1).

Sun Cluster uses agents to simplify cluster configuration. Each type of resource supported in a cluster is associated with an agent. An agent is an installed program designed to control a particular resource type. For Sun Cluster to bring a certain resource online, it does not need to understand it, but simply pass the online command to the agent. Sun Cluster has Oracle, DB2, Informix®, and SyBase agents. Many other enterprise agents are also available. Some of these agents come with the base cluster software, and some require additional purchase. Sun Cluster can use the Solaris Volume Manager or the VERITAS Volume Manager.

The Resource Group manager handles high availability and scalability in Sun Cluster. It manages the resource types (also known as data services), resource groups and resources.

Sun Cluster supports both Active/Passive failover and Active/Active availability. Sun Cluster uses the terms failover and scalable to describe these activities.

Sun Cluster can: - Reduce or eliminate system downtime because of software or hardware failures.

- Ensure availability of data and applications to users, regardless of the kind of failure that would normally take down a single-server system.

- Increase application throughput by enabling services to scale to additional processors by adding nodes to the cluster.

- Provide enhanced availability of the system by enabling you to perform maintenance without shutting down the entire cluster.

Sun Cluster configurations tolerate the following types of single-point failures:

Server operating environment failure because of a crash or a panic

Data service failure

Server hardware failure

Network interface failure

Disk media failure

As depicted in Figure 13-1, clients access the primary system.

Figure 13-1 Sun Cluster setup: running on primary machine

In the case of a failure, the clients failover to the second machine as shown in Figure 13-2.

Figure 13-2 Sun Cluster setup: primary machine fails, failover to secondary machine

You can find more information about Sun Cluster software at:

http://www.sun.com/clusters

Notes:
-	The current version of Sun Cluster is 3.1 8/05.

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