General Planning

A clear understanding of your high availability objectives will help you to define your hardware requirements and design your system. Use the following questions as a guide for general planning:

What applications must continue to be available in the event of a failure?
What system resources (processing power, networking, SPU, memory, disk space) are needed to support these applications?
How will these resources be distributed among the nodes in the cluster during normal operation?
How will these resources be distributed among the nodes of the cluster in all possible combinations of failures, especially node failures?
How will resources be distributed during routine maintenance of the cluster?
What are the networking requirements? Are all networks and subnets available?
Have you eliminated all single points of failure? For example:
- network points of failure.
- disk points of failure.
- electrical points of failure.
- application points of failure.

Serviceguard Memory Requirements

Serviceguard requires approximately 15.5 MB of lockable memory.

Planning for Expansion

When you first set up the cluster, you indicate a set of nodes and define a group of packages for the initial configuration. At a later time, you may wish to add additional nodes and packages, or you may wish to use additional disk hardware for shared data storage. If you intend to expand your cluster without the need to bring it down, careful planning of the initial configuration is required. Use the following guidelines:

Remember the rules for cluster locks when considering expansion. A one-node cluster does not require a cluster lock. A two-node cluster must have a cluster lock. In clusters larger than 3 nodes, a cluster lock is strongly recommended. If you have a cluster with more than 4 nodes, you can use a quorum server but a cluster lock disk is not allowed.
Networks should be pre-configured into the cluster configuration if they will be needed for packages you will add later while the cluster is running.
Resources monitored by EMS (Event Monitoring Service) should be pre-configured into the cluster configuration if they will be needed for packages you will add later while the cluster is running. Once a resource dependency is configured for any package in the cluster, it will always be available for later packages to use. However, you cannot add a never-before-configured resource to a package while the package is running.

Refer to the chapter on “Cluster and Package Maintenance” for more information about changing the cluster configuration dynamically, that is, while the cluster is running.

General Planning

Technical documentation

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Serviceguard Memory Requirements

Planning for Expansion