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Chapter 1: Overview of the Planning Process
This chapter provides an overview of the planning and installation process. This chapter contains the following sections:
Overview of the Planning Process Goals
Your major goal throughout the planning process is to eliminate single points of failure. A single point of failure exists when a critical cluster function is provided by a single component. If that component fails, the cluster has no other way of providing that function, and the application or service dependent on that component becomes unavailable.
For example, if all the data for a critical application resides on a single disk, and that disk fails, that disk is a single point of failure for the entire cluster. Clients cannot access that application until the data on the disk is restored. Likewise, if dynamic application data is stored on internal disks rather than on external disks, it is not possible to recover an application by having another cluster node take over the disks. Therefore, identifying necessary logical components required by an application, such as filesystems and directories (which could contain application data and configuration variables), is an important prerequisite for planning a successful cluster.
Realize that, while your goal is to eliminate all single points of failure, you may have to make some compromises. There is usually a cost associated with eliminating a single point of failure. For example, purchasing an additional hardware device to serve as backup for the primary device increases cost. The cost of eliminating a single point of failure should be compared against the cost of losing services should that component fail. Again, the purpose of the HACMP is to provide a cost-effective, highly available computing platform that can grow to meet future processing demands.
Note: It is important that failures of cluster components be remedied as soon as possible. Depending on your configuration, it may be possible for HACMP to handle a second failure, due to lack of resources.
Planning Guidelines
Designing the cluster that provides the best solution for your organization requires careful and thoughtful planning. In fact, adequate planning is the key to building a successful HACMP cluster. A well-planned cluster is easier to install, provides higher application availability, performs better, and requires less maintenance than a poorly planned cluster.
For a critical application to be highly available, none of the associated resources should be a single point of failure. As you design an HACMP cluster, your goal is to identify and address all potential single points of failure. Questions to ask include:
What application services are required to be highly available? What is the priority of these services? What is the cost of a failure compared to the necessary hardware to eliminate the possibility of this failure? What is the maximum number of redundant hardware and software components that HACMP can support? (See Eliminating Single Points of Failure: Configuring Redundant Components Supported by HACMP). What is the required availability of these services? Do they need to be available 24 hours a day, seven days a week, or is eight hours a day, five days a week sufficient? What could happen to disrupt the availability of these services? What is the allotted time for replacing a failed resource? What is an acceptable degree of performance degradation while operating after a failure? Which failures will by automatically detected as cluster events? Which failures need to have custom code written to detect the failure and trigger a cluster event? What is the skill level of the group implementing the cluster? The group maintaining the cluster? To plan, implement, and maintain a successful HACMP cluster requires continuing communication among many groups within your organization. Ideally, you should assemble the following representatives (as applicable) to aid in HACMP planning sessions:
Network administrator System administrator Database administrator Application programming Support personnel End users. HACMP supports a variety of configurations, providing you with a great deal of flexibility. For information about designing for the highest level of availability for your cluster, see the IBM whitepaper High Availability Cluster Multiprocessing Best Practices at the following URL:
htttp://www.ibm.com/servers/eserver/clusters/whitepapers/hacmp_bestpractices.html
Eliminating Single Points of Failure: Configuring Redundant Components Supported by HACMP
The HACMP software provides numerous options to avoid single points of failure. The following table summarizes potential single points of failure and describes how to eliminate them by configuring redundant hardware and software cluster components:
Overview of the Planning Tools
This section describes the planning tools (worksheets) supplied by HACMP. Use these tools according to the processes described in Overview of the Planning Process. Each stage of the cluster planning process has worksheets that correspond with your planning tasks, to aid you in the planning process.
Paper Worksheets
The paper worksheets, which you fill out by hand and have physically nearby to refer to as you configure your cluster, are located in Appendix A: Planning Worksheets.
Online Planning Worksheets Application
The Online Planning Worksheets application is an online version of the paper worksheets. The application provides the following benefits:
You may enter data into the worksheets as you plan the cluster and store the worksheets online At the end of the planning process, HACMP enables you to convert your planning data into an actual HACMP cluster configuration. For more information, see Chapter 9: Using Online Planning Worksheets. Overview of the Planning Process
This section describes the steps for planning an HACMP cluster.
Step 1: Planning for Highly Available Applications
In this step, you plan the core of the cluster—the applications to be made highly available, the types of resources they require, the number of nodes, shared IP addresses, and a mode for sharing disks (non-concurrent or concurrent access). Your goal is to develop a high-level view of the system that serves as a starting point for the cluster design. After making these initial decisions, record them on the Application Worksheet and start to draw a diagram of the cluster. Chapter 2: Initial Cluster Planning describes this step of the planning process.
Step 2: Planning Cluster Topology
In this step, you decide on names for the cluster and the nodes. Optionally, you also decide on names for sites and decide which nodes belong to which site. Chapter 2: Initial Cluster Planning describes this step of the planning process.
Step 3: Planning Cluster Network Connectivity
In this step, you plan the networks that connect the nodes in your system. You first examine issues relating to TCP/IP and point-to-point networks in an HACMP environment. Next, you decide on the networks you will use, record your decision on the networks worksheet and add the networks to the cluster diagram. Chapter 3: Planning Cluster Network Connectivity describes this step of the planning process.
Step 4: Planning Shared Disk Devices
In this step, you plan the shared disk devices for the cluster. You decide which disk storage technologies you will use in your cluster, and examine issues relating to those technologies in the HACMP environment. Complete the disk worksheets and add the shared disk configuration to your diagram. Chapter 4: Planning Shared Disk and Tape Devices describes this step of the planning process.
You also decide whether you will be using enhanced concurrent mode volume groups in non-concurrent resource groups: For such volume groups, a faster disk takeover mechanism is used in HACMP. For more information, see Chapter 5: Planning Shared LVM Components.
Step 5: Planning Shared LVM Components
In this step, you plan the shared volume groups for the cluster. You first examine issues relating to LVM components in an HACMP environment, and then you fill out worksheets describing physical and logical storage. You may want to include planning for disaster recovery with cross-site LVM mirroring in this step. Chapter 5: Planning Shared LVM Components describes this step of the planning process.
Step 6: Planning Resource Groups
Planning resource groups incorporates all of the information you have generated in the previous steps. In addition, you should decide whether to use dependent resource groups or particular runtime policies for keeping certain related resource groups on the same node, on different nodes, or on the same site. Chapter 6: Planning Resource Groups describes this step of the planning process. Also see Appendix C: Resource Group Behavior During Cluster Events in the Administration Guide for further information that may help you plan your configuration.
Step 7: Planning Cluster Event Processing
In this step, you plan the event processing for your cluster. Chapter 7: Planning for Cluster Events describes this step of the planning process.
Step 8: Planning HACMP Clients
In this step, you examine issues relating to HACMP clients. Chapter 8: Planning for HACMP Clients describes this step of the planning process.
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