An Introduction to the New IBM eServer pSeries High Performance Switch

Chapter 3. Application considerations 97

3.3 HACMP

The following sections provide an overview of the benefits of using High Performance Switch

in an HACMP environment.

3.3.1 HACMP overview

HACMP is a tool for building UNIX-based mission-critical computing platforms. HACMP

software ensures that critical resources, such as applications, are available for processing.

HACMP has two major components: high availability (HA) and cluster multi-processing

(CMP).

The primary reason for creating HACMP clusters is to provide a highly available environment

for mission-critical applications. For example, an HACMP cluster could run a database server

program that services client applications. The clients send queries to the server program,

which responds to their requests by accessing a database stored on a shared external disk.

In an HACMP cluster, the applications are put under HACMP control to ensure the availability

of these applications. HACMP takes measures to ensure that the applications remain

available to client processes even if a component in a cluster fails. To ensure availability, in

case of a component failure, HACMP moves the application (along with resources that ensure

access to the application) to another node in the cluster.

3.3.2 Role of HACMP

HACMP helps you with each of the following:

 The HACMP planning process and documentation include tips and advice on the best

practices for installing and maintaining a highly available HACMP cluster.

 Once the cluster is operational, HACMP provides the automated monitoring and recovery

for all of the resources on which the application depends.

 HACMP provides a full set of tools for maintaining the cluster while keeping the application

available to clients.

HACMP lets you:

 Set up an HACMP environment using online planning worksheets to simplify the initial

planning and setup.

 Ensure high availability of applications by eliminating single points of failure in an HACMP

environment.

 Leverage high availability features available in AIX.

 Manage how a cluster handles component failures.

 Secure cluster communications.

 Set up fast disk takeover for volume groups managed by the Logical Volume Manager

(LVM).

 Manage event processing for an HACMP environment.

 Monitor HACMP components and diagnose problems that may occur.

3.3.3 Physical components of an HACMP cluster

HACMP provides a highly available environment by identifying a set of resources essential to

uninterrupted processing, and by defining a protocol that nodes use to collaborate to ensure

98 An Introduction to the New IBM Eserver pSeries High Performance Switch

that these resources are available. HACMP extends the clustering model by defining

relationships among cooperating processors, where one processor provides the service

offered by a peer should the peer be unable to do so.

An HACMP cluster is made up of the following physical components:

 Nodes

 Shared external disk devices

 Networks

 Network interfaces

 Clients

The HACMP software allows you to combine physical components into a wide range of

cluster configurations, providing you with flexibility in building a cluster that meets your

processing requirements. Figure 3-14 shows one example of an HACMP cluster. Other

HACMP clusters could look very different, depending on the number of processors, the

choice of networking and disk technologies, and so on.

Figure 3-14 Example HACMP cluster scenario

Nodes

Nodes form the core of an HACMP cluster. A node is a processor that runs both AIX and the

HACMP software. HACMP supports pSeries uniprocessor and symmetric multiprocessor

(SMP) systems (including LPARs) and the Scalable POWERparallel processor (SP) systems

as cluster nodes. To the HACMP software, an SMP system looks just like a uniprocessor.

SMP systems provide a cost-effective way to increase cluster throughput. Each node in the

cluster can be a large SMP machine, extending an HACMP cluster far beyond the limits of a

single system and allowing thousands of clients to connect to a single database.

In an HACMP cluster, up to 32 nodes cooperate to provide a set of services or resources to

other entities. Clustering these servers to back up critical applications is a cost-effective high

availability option. A business can use more of its computing power while ensuring that its

Private LAN

Disk buses

Public LAN1

Public LAN2

Clients

Shared disk space (protected)

Nodes