Introduction to IBM High-Availability Cluster Solutions

Chapter 1. Introduction to IBM High-Availability Cluster Solutions

A cluster  is a type of parallel or distributed system that consists of interconnected computers used as a single, unified computing resource.
In other words, a group of computers linked together in such a way that they share and manage a set of resources that can support a number of users at the same time.

This high-availability clustering solution  is based on a two-node cluster, where both nodes, or servers, can access the same storage devices, but only one server at a time controls the storage devices shared by both servers.
If one server fails, the remaining server automatically assumes control of the resources that the failed server was using, while still controlling its own resources at the same time.
The failed server can then be repaired offline without the loss of time or work efficiency, because access to that server's data and applications is still available.

Once the failed server is operational again, it can be placed back into the cluster, the resources are reallocated between the two servers and the cluster can then resume normal operations.

IBM high-availability cluster solutions, as discussed in this manual, use IBM ServeRAID-3H Ultra2 SCSI Adapters (ServeRAID-3L Ultra2 SCSI adapters do not support clustering) and IBM expansion enclosures, such as the IBM Enterprise Expansion Enclosure (Model 3518), the IBM PC Server 3519 Rack Expansion Enclosure, the IBM Netfinity EXP10 Rack Expansion Enclosure or the IBM Netfinity EXP15 Rack Expansion Enclosure.

IBM high-availability cluster solutions can be installed using one of the following:

The following figures show an example of a simple high-availability clustering solution.
Figure 1 shows a high-level view of a cluster. Figure 2 shows a more detailed view of a cluster.


The solution you use for your installation depends on your own specific requirements.
For more information about requirements and types of installations, refer to the
'IBM Shared Disk Clustering Hardware Reference', Part Number 33L3945.

This publication can be found on the IBM World Wide Web page at

Once you are on the web page, perform a search for the clustering information.

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