SherbyNet - /page/wikibook/entry.mu

Micron Document

<!DOCTYPE html>

<title>Continuous availability</title>

</head>

<span id="openzim-page-title" class="mw-page-title-main"><span class="mw-page-title-main">Continuous availability</span></span>

</h1>

</header>

<div id="mw-content-text" class="mw-body-content mw-content-ltr" lang="en" dir="ltr"><div class="mw-content-ltr mw-parser-output" lang="en" dir="ltr"><p><b>Continuous availability</b> is an approach to <a href="Computer_system" class="mw-redirect" title="Computer system">computer system</a> and application design that protects users against downtime, whatever the cause and ensures that users remain connected to their documents, data files and business applications. Continuous availability describes the information technology methods to ensure <a href="Business_continuity" class="mw-redirect" title="Business continuity">business continuity</a>.<sup id="cite_ref-1" class="reference"><a href="#cite_note-1"><span class="cite-bracket">[</span>1<span class="cite-bracket">]</span></a></sup>

</p><p>In early days of computing, availability was not considered business critical. With the increasing use of <a href="Mobile_computing" title="Mobile computing">mobile computing</a>, global access to online business transactions and business-to-business communication, continuous availability is increasingly important based on the need to support customer access to information systems.<sup id="cite_ref-2" class="reference"><a href="#cite_note-2"><span class="cite-bracket">[</span>2<span class="cite-bracket">]</span></a></sup>

</p><p>Solutions to continuous availability exists in different forms and implementations depending on the software and hardware manufacturer. The goal of the discipline is to reduce the user or business application downtime, which can have a severe impact on business operations. Inevitably, such downtime can lead to loss of productivity, loss of revenue, customer dissatisfaction and ultimately can damage a company's reputation.

</p>

<div class="mw-heading mw-heading2"><h2 id="Degrees_of_availability">Degrees of availability</h2></div>

<p>The terms <a href="High_availability" title="High availability">high availability</a>, continuous operation, and continuous availability are generally used to express how available a system is.<sup id="cite_ref-3" class="reference"><a href="#cite_note-3"><span class="cite-bracket">[</span>3<span class="cite-bracket">]</span></a></sup><sup id="cite_ref-4" class="reference"><a href="#cite_note-4"><span class="cite-bracket">[</span>4<span class="cite-bracket">]</span></a></sup> The following is a definition of each of these terms.

</p><p><b>High availability</b>

refers to the ability to avoid unplanned outages by eliminating <a href="Single_point_of_failure" title="Single point of failure">single points of failure</a>.

This is a measure of the reliability of the hardware, operating system, middleware, and database manager software.

Another measure of high availability is the ability to minimize the effect of an unplanned outage by masking the outage from the end users.

This can be accomplished by providing redundancy or quickly restarting failed components.

</p><p>Availability is usually expressed as a percentage of uptime in a given year:

</p>

<th>Availability

</th>

<th>Downtime per year

</th></tr>

<tr>

<td>99.9%

</td>

<td>8.76 hours

</td></tr>

<tr>

<td>99.99%

</td>

<td>1 hour

</td></tr>

<tr>

<td>99.999%

</td>

<td>5 minutes

</td></tr></tbody></table>

<p>When defining such a percentage it needs to be specified if it applies to the hardware, the <a href="IT_infrastructure" title="IT infrastructure">IT infrastructure</a> or the business application on top.<sup id="cite_ref-5" class="reference"><a href="#cite_note-5"><span class="cite-bracket">[</span>5<span class="cite-bracket">]</span></a></sup>

</p><p><b>Continuous operation</b> refers to the ability to avoid planned outages.

For continuous operation there must be ways to perform necessary administrative work, like hardware and software maintenance, upgrades, and platform refreshes while the business application remains available to the end users. This is accomplished by providing multiple servers and switching end users to an available server at times when one server is made unavailable.

Note that a system running in continuous operation is not necessarily operating with high availability because an excessive number of unplanned outages could compromise this.

</p><p><b>Continuous availability</b> combines the characteristics of high availability and continuous operation to provide the ability to keep the business application running without any noticeable downtime.

</p>

<div class="mw-heading mw-heading2"><h2 id="Types_of_outages">Types of outages</h2></div>

<p><b>Planned outages</b> are deliberate and are scheduled at a convenient time. These involve such activities as:

- Hardware installation or maintenance

- Software maintenance or upgrades of the operating system, the middleware, the database server or the business application

- Database administration such as offline backup, or offline reorganization

</p><p><b>Unplanned outages</b> are unexpected outages that are caused by the failure of any system component.

They include hardware failures, software issues, or people and process issues.

</p>

<div class="mw-heading mw-heading2"><h2 id="History">History</h2></div>

<p>Various commercially viable examples exist for hardware/software implementations. These include:

</p>

<li><a href="BitTorrent" title="BitTorrent">BitTorrent</a></li>

<li><a href="Cockroach_Labs" class="mw-redirect" title="Cockroach Labs">CockroachDB</a></li>

<li><a href="Dovecot_(software)" title="Dovecot (software)">Dovecot</a></li>

<li><a href="IBM_Parallel_Sysplex" title="IBM Parallel Sysplex">IBM Parallel Sysplex</a></li>

<li>MariaDB Xpand</li>

<li><a href="Stratus_VOS" title="Stratus VOS">Stratus</a></li>

<li><a href="Tandem_computer" class="mw-redirect" title="Tandem computer">Tandem NonStop Computers</a></li>

<li><a href="YugabyteDB" title="YugabyteDB">YugabyteDB</a></li></ul>

<ul><li><a href="Business_continuity_planning" title="Business continuity planning">Business continuity planning</a></li>

<li><a href="IT_disaster_recovery" title="IT disaster recovery">Disaster recovery</a></li>

<li><a href="High-availability_cluster" title="High-availability cluster">High-availability cluster</a></li>

<li><a href="Fault-tolerant_system" class="mw-redirect" title="Fault-tolerant system">Fault-tolerant system</a></li>

<li><a href="Service_Availability_Forum" title="Service Availability Forum">Service Availability Forum</a></li></ul>

<div class="mw-heading mw-heading2"><h2 id="References">References</h2></div>

/* start https://en.wikipedia.org/ */

.mw-parser-output .reflist{margin-bottom:0.5em;list-style-type:decimal}@media screen{.mw-parser-output .reflist{font-size:90%}}.mw-parser-output .reflist .references{font-size:100%;margin-bottom:0;list-style-type:inherit}.mw-parser-output .reflist-columns-2{column-width:30em}.mw-parser-output .reflist-columns-3{column-width:25em}.mw-parser-output .reflist-columns{margin-top:0.3em}.mw-parser-output .reflist-columns ol{margin-top:0}.mw-parser-output .reflist-columns li{page-break-inside:avoid;break-inside:avoid-column}.mw-parser-output .reflist-upper-alpha{list-style-type:upper-alpha}.mw-parser-output .reflist-upper-roman{list-style-type:upper-roman}.mw-parser-output .reflist-lower-alpha{list-style-type:lower-alpha}.mw-parser-output .reflist-lower-greek{list-style-type:lower-greek}.mw-parser-output .reflist-lower-roman{list-style-type:lower-roman}

/* end https://en.wikipedia.org/ */

</style><div class="reflist">

<li id="cite_note-1"><span class="mw-cite-backlink"><b><a href="#cite_ref-1">^</a></b></span> <span class="reference-text">Business Continuity: Delivering Data and Applications Through Continuous Availability, A META Group White Paper, June 2003 <a rel="nofollow" class="external autonumber" href="http://m.sybase.com/content/1025175/BusinessContinuity_whitepaper.pdf">[1]</a> <a rel="nofollow" class="external text" href="https://web.archive.org/web/20120425112312/http://m.sybase.com/content/1025175/BusinessContinuity_whitepaper.pdf">Archived</a> 2012-04-25 at the <a href="Wayback_Machine" title="Wayback Machine">Wayback Machine</a></span>

</li>

<li id="cite_note-2"><span class="mw-cite-backlink"><b><a href="#cite_ref-2">^</a></b></span> <span class="reference-text">Gartner Survey Shows IT Availability Remain Top Priorities for U.S. IT Services Buyers, September 2010 <a rel="nofollow" class="external autonumber" href="https://web.archive.org/web/20100703110120/http://www.gartner.com/it/page.jsp?id=1392715">[2]</a></span>

</li>

<li id="cite_note-3"><span class="mw-cite-backlink"><b><a href="#cite_ref-3">^</a></b></span> <span class="reference-text">High availability (again) versus continuous availability, IBM WebSphere Developer Technical Journal, April 14, 2010 <a rel="nofollow" class="external autonumber" href="http://www.ibm.com/developerworks/websphere/techjournal/1004_webcon/1004_webcon.html">[3]</a></span>

</li>

<li id="cite_note-4"><span class="mw-cite-backlink"><b><a href="#cite_ref-4">^</a></b></span> <span class="reference-text">Bob Dickerson: Service Recovery &

Availability, IEEE Computer Society, 2010 Meeting <a rel="nofollow" class="external autonumber" href="https://ewh.ieee.org/r1/rochester/computer/2010/20100610/PlatformAvailabilityPresentation.IEEE.pdf">[4]</a></span>

</li>

<li id="cite_note-5"><span class="mw-cite-backlink"><b><a href="#cite_ref-5">^</a></b></span> <span class="reference-text"><a rel="nofollow" class="external text" href="http://www.itsmsolutions.com/newsletters/DITYvol2iss47.pdf">itSM Solutions Newsletter December 2006: The Paradox of the 9s</a></span>

</li>

</ol></div></div>

<div class="mw-heading mw-heading2"><h2 id="External_links">External links</h2></div>

<ul><li><a rel="nofollow" class="external text" href="http://www.continuitycentral.com/highca.htm">Continuity Central</a></li>

<li><a rel="nofollow" class="external text" href="https://web.archive.org/web/20091205203532/http://msmvps.com/blogs/clusterhelp/archive/2005/08/05/61708.aspx">Continuous Availability Blog</a></li>

<li><a rel="nofollow" class="external text" href="http://www.computerweekly.com/Articles/2010/03/30/240750/Continuous-Availability-for-Microsoft-SharePoint-Farms-White.htm">Continuous Availability for SharePoint</a></li>

<li><a rel="nofollow" class="external text" href="http://publibfp.dhe.ibm.com/epubs/pdf/iapacs0a.pdf">Business Continuity for SAP on IBM System z</a></li>

<li><a rel="nofollow" class="external text" href="http://www.eventhelix.com/RealtimeMantra/FaultHandling/reliability_availability_basics.htm">Reliability and Availability Basics</a></li>

<li><a rel="nofollow" class="external text" href="https://www.techrepublic.com/article/it-should-establish-realistic-availability-requirements/1060286">TechRepublic: IT should establish realistic availability requirements</a></li>

<li>US Patent 5027269, "Method and apparatus for providing continuous availability of applications in a computer network", 1991; <a href="IBM" title="IBM">IBM</a></li></ul></div><div><div class="zim-footer">

This article is issued from <a class="external text" title="Last edited on 2024-10-17" href="https://en.wikipedia.org/wiki/?title=Continuous_availability&oldid=1251744178">Wikipedia</a>. The text is available under <a class="external text" href="https://creativecommons.org/licenses/by-sa/4.0/deed.en">Creative Commons Attribution-Share Alike 4.0</a> unless otherwise noted. Additional terms may apply for the media files.

</div>

</div></div>

</div>

</main>

</div>

</body></html>