109 lines
7.8 KiB
HTML
109 lines
7.8 KiB
HTML
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<?xml version="1.0" encoding="UTF-8"?>
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<!DOCTYPE html
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PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
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<html lang="en-us" xml:lang="en-us">
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<head>
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<meta name="DC.Type" content="concept" />
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<meta name="DC.Title" content="Availability concepts" />
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<meta name="abstract" content="Before you can plan for the availability of your system, it is important for you to understand some of the concepts associated with availability." />
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<meta name="description" content="Before you can plan for the availability of your system, it is important for you to understand some of the concepts associated with availability." />
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<meta name="copyright" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Rights.Owner" content="(C) Copyright IBM Corporation 1998, 2006" />
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<meta name="DC.Format" content="XHTML" />
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<meta name="DC.Language" content="en-us" />
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<!-- All rights reserved. Licensed Materials Property of IBM -->
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<!-- Use, duplication or disclosure restricted by -->
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<!-- GSA ADP Schedule Contract with IBM Corp. -->
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<link rel="stylesheet" type="text/css" href="./ibmdita.css" />
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<link rel="stylesheet" type="text/css" href="./ic.css" />
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<title>Availability concepts</title>
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</head>
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<body id="rzalwconcepts"><a name="rzalwconcepts"><!-- --></a>
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<img src="./delta.gif" alt="Start of change" /><!-- Java sync-link --><script language="Javascript" src="../rzahg/synch.js" type="text/javascript"></script>
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<h1 class="topictitle1">Availability concepts</h1>
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<div><p>Before you can plan for the availability of your system, it is
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important for you to understand some of the concepts associated with availability.</p>
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<p>Businesses and their IT operations that support them must determine which
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solutions and technologies will address their business needs. In the case
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of business continuity requirements, the task is equally daunting. Detailed
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business continuity requirements must be developed and documented, the solution
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types identified, and the solution choices evaluated. This is a challenging
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task due in part to the complexity of the problem. </p>
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<p><em>Business continuity</em> is the capability of a business to withstand
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outages, which are times when the system is unavailable, and to operate important
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services normally and without interruption in accordance with predefined service-level
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agreements. To achieve a given desired level of business continuity, a collection
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of services, software, hardware, and procedures must be selected, described
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in a documented plan, implemented, and practiced regularly. The business continuity
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solution must address the data, the operational environment, the applications,
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the application hosting environment, and the end-user interface. All must
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be available to deliver a good, complete business continuity solution. Your
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business continuity plan includes disaster recovery (DR) and high availability
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(HA). </p>
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<p>Disaster recovery (DR) provides a plan in the event of a complete outage
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at the production site of your business, such as during a natural disaster.
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DR may provide a set of resources, plans, services, and procedures used to
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recover important applications and to resume normal operations from a remote
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site. This <dfn class="term">Disaster Recovery Plan</dfn> includes a stated disaster
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recovery goal (for example, resume operations within eight hours) and addresses
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acceptable levels of degradation. </p>
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<p>Another major aspect of business continuity goals for many customers is <dfn class="term">high
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availability</dfn>, which is the ability to withstand all outages (planned,
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unplanned, and disasters) and to provide continuous processing for all important
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applications. The ultimate goal is for the outage time to be less than .001%
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of total service time. The differences between high availability and disaster
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recovery typically include more demanding recovery time objectives (seconds
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to minutes) and more demanding recovery point objectives (zero end user disruption). </p>
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<p>Availability is measured in terms of <dfn class="term">outages</dfn>, which are periods
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of time when the system is not available to users. During a <dfn class="term"> planned
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outage</dfn> (also called a scheduled outage), you deliberately make your
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system unavailable to users. You might use a scheduled outage to run batch
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work, back up your server, or apply fixes. </p>
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<p>Your <dfn class="term">backup window</dfn> is the amount of time that your server
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can be unavailable to users while you perform your backup operations. Your
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backup window is a scheduled outage that usually occurs in the night or on
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a weekend when your system has less traffic.</p>
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<p>An <dfn class="term">unplanned outage</dfn> (also called an unscheduled outage) is
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usually caused by a failure. You can recover from some unplanned outages (such
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as disk failure, system failure, power failure, program failure, or human
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error) if you have an adequate backup strategy. However, an unplanned outage
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that causes a complete system loss, such as a tornado or fire, requires you
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to have a detailed disaster recovery plan in place in order to recover.</p>
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<p><img src="./delta.gif" alt="Start of change" />High availability solutions provide fully automated failover
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to a backup system to ensure continuous operation for end users and applications.
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These HA solutions must provide an immediate recovery point and ensure that
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the time of recovery is faster than a non-HA solution. <img src="./deltaend.gif" alt="End of change" /></p>
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<p>Unlike with disaster recovery, where entire systems experience an outage,
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high availability solutions can be customized to individual critical
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resources within a system, for example a specific application instance. On
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the i5/OS™ system,
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the high availability solution is based on cluster technology. You can use
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i5/OS Clusters as a method to avoid the impacts of both planned and unplanned
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outages. Even though you still have the outage of the server, the business
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function will not be impacted by the outage. A <dfn class="term">cluster</dfn> is a
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collection of interconnected complete systems used as a single, unified resource.
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The cluster provides a coordinated, distributed process across the systems
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to deliver the solution. This results in higher levels of availability, some
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horizontal growth and simpler administration across the enterprise. For a
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complete solution, you must address the operational environment, the application
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hosting environment, application resilience, and the end-user interfaces in
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addition to providing data resilience mechanisms. Clusters focus on all aspects
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of the complete solution. The integrated cluster resource services enable
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you to define a cluster of systems and the set of resources that should be
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protected against outages. Cluster resource services detect outage conditions
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and coordinate automatic movement of critical resources to a backup system.</p>
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</div>
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<div>
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<div class="familylinks">
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<div class="parentlink"><strong>Parent topic:</strong> <a href="rzalwoverview.htm" title="In today's fast-paced Internet environment, it is crucial that your data and applications be available to you when you need them. If your customers cannot access your Web site because your system is down, they may go to your competitors instead.">Availability roadmap</a></div>
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</div>
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</div>
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<img src="./deltaend.gif" alt="End of change" /></body>
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</html>
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