Tier centres | Worldwide LHC Computing Grid

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data-drupal-link-system-path="node/20">History of WLCG</a> </li> </ul> </li> <li> <a href="/tiers" data-drupal-link-system-path="node/21">Tiers</a> </li> <li> <a href="/structure" data-drupal-link-system-path="node/11">Structure</a> </li> <li> <a href="/get-involved" data-drupal-link-system-path="node/10">Get Involved</a> </li> <li> <a href="/resources" data-drupal-link-system-path="node/12">Resources</a> </li> </ul> </div>  </div>  </nav> </nav> </div> </div> </div> </div> </header> <main role="main"> <a id="main-content" tabindex="-1"></a> <div class="container"> <div class="wrapper-center col-md-12 col-sm-12 col-xs-12"> <div class="region region-content"> <div data-drupal-messages-fallback class="hidden"></div> <h1 class="page-header"> <span property="dc:title">Tier centres</span> </h1> <article data-history-node-id="4" about="/tier-centres" typeof="foaf:Document" class="page full clearfix"> <span property="dc:title" content="Tier centres" class="hidden"></span> <span property="sioc:num_replies" datatype="xsd:integer" class="hidden"></span> <div class="content"> <div property="content:encoded" class="field field--name-body field--type-text-with-summary field--label-hidden field--item"><p>WLCG is made up of four layers, or "tiers"; 0, 1, 2 and 3. Each tier provides a specific set of services.</p> <p><img alt="WLCG Tiers" data-entity-type="file" data-entity-uuid="dcb4d088-f32e-47b9-a90f-290b5beab23b" src="/sites/default/files/inline-images/WLCG-Tiers-2021_v3.png" style="height:50%; width:50%;" class="align-left" width="1200" height="1125" loading="lazy"></p> <h3>Tier-0</h3> <p>This is the <strong>CERN Data Centre</strong>, which is located in Geneva, Switzerland. All data from the LHC passes through the central CERN hub, but CERN only provides around 20% of the total compute capacity.</p> <p>Tier 0 is responsible for the safe-keeping of the raw data (first copy), first pass reconstruction, distribution of raw data and reconstruction output to the Tier 1s, and reprocessing of data during LHC down-times.</p> <h3>Tier 1</h3> <p>These are <strong>thirteen large computer centres</strong> with sufficient storage capacity and with round-the-clock support for the Grid. They are responsible for the safe-keeping of a proportional share of raw and reconstructed data, large-scale reprocessing and safe-keeping of corresponding output, distribution of data to Tier 2s and safe-keeping of a share of simulated data produced at these Tier 2s.</p> <h3>Tier 2</h3> <p>The Tier 2s are typically <strong>universities and other scientific institutes</strong>, which can store sufficient data and provide adequate computing power for specific analysis tasks. They handle analysis requirements and proportional share of simulated event production and reconstruction.</p> <p>There are currently around 160 Tier 2 sites covering most of the globe.</p> <h3>Tier 3</h3> <p>Individual scientists will access these facilities through local (also sometimes referred to as Tier 3) computing resources, which can consist of local clusters in a University Department or even just an individual PC. There is no formal engagement between WLCG and Tier 3 resources.</p> <h2>World map of the current WLCG sites (Tiers 0, 1 & 2)</h2> <p><iframe height="480" src="https://www.google.com/maps/d/embed?mid=1uqabSfnzpBZ_fS_RfBFhRXx9nws" width="640"></iframe></p> </div> <section> </section> </div> </article> </div> </div> </div> </main> <footer role="contentinfo"> <div class="row cern-footer"> <div class="col-xs-12 col-sm-3 col-md-3 col-lg-3 footer-first-col"> <div class="region region-footercolumn1"> <section id="block-elegant-theme-block-7" class="block block-block-content block-block-contente2dcd96d-433b-4933-89de-a7ce90dcf95b clearfix"> <h2 class="block-title">Contact</h2> <div class="field field--name-body field--type-text-with-summary field--label-hidden field--item"><p><strong>WLCG Office</strong><br> Mailbox <span>M32100</span><br> IT Department, CERN<br> CH-1211 Geneva, Switzerland</p> <p><strong>e-mail:</strong> <a href="mailto:lcg.office@cern.ch">lcg.office@cern.ch</a></p> </div> </section> </div> </div> <div class="col-xs-12 col-sm-8 col-md-8 col-lg-8 footer-second-col"> <div class="row">  <div class="col-sm-5 col-md-4 col-md-offset-0 col-lg-4 col-lg-offset-0"> <div class="region region-footercolumn2"> <section id="block-collaborationwebsite" class="block block-block-content block-block-content93e6e86f-e814-44c2-b66c-bae5f92ddca4 clearfix"> <h2 class="block-title">Collaboration website</h2> <div class="field field--name-body field--type-text-with-summary field--label-hidden field--item"><p>The WLCG technical website is at</p> <p><a href="http://wlcg.web.cern.ch/">http://wlcg.web.cern.ch/</a></p> </div> </section> </div> </div>  <div class="col-sm-6 col-sm-offset-1 col-md-4 col-md-offset-0 col-lg-4"> <div class=" mb-4"> </div> </div>  <div class="col-sm-6 col-sm-offset-6 col-md-4 col-md-offset-0 col-lg-4 col-lg-offset-0"> <div class=" mb-4"> </div> </div> </div> </div> <div class="col-xs-1 col-sm-1 col-md-1 col-lg-1 footer-last-logo"> <a href="https://home.cern/" title="CERN" target="_blank"><img src="/themes/custom/cern-theme/logo.svg" alt="CERN"/></a> </div> </div> <div class="copy-wrapper light"> <a href="https://copyright.web.cern.ch/"> Copyright </a>  © 2025 CERN</div> </footer> </div> <script type="application/json" data-drupal-selector="drupal-settings-json">{"path":{"baseUrl":"\/","pathPrefix":"","currentPath":"node\/4","currentPathIsAdmin":false,"isFront":false,"currentLanguage":"en"},"pluralDelimiter":"\u0003","suppressDeprecationErrors":true,"ajaxPageState":{"libraries":"eJxljFEKxDAIRC-U1iMV00jIYmJQW7a336aBZWG_hjdPJ4q4uWKHLl1O0hC_jYuwlx520rYlOjdz9MNg8HLzMnn6cRxR4RceE9EIMktEvh8uLi0__c6E7U-IEiQ9OvKaCrLkFV_4DhVdqsCMYJc5VRjLH6dESzU","theme":"cernclean","theme_token":null},"ajaxTrustedUrl":[],"matomo":{"disableCookies":false,"trackMailto":true},"bootstrap":{"forms_has_error_value_toggle":1,"modal_animation":1,"modal_backdrop":"true","modal_focus_input":1,"modal_keyboard":1,"modal_select_text":1,"modal_show":1,"modal_size":"","popover_enabled":1,"popover_animation":1,"popover_auto_close":1,"popover_container":"body","popover_content":"","popover_delay":"0","popover_html":0,"popover_placement":"right","popover_selector":"","popover_title":"","popover_trigger":"click","tooltip_enabled":1,"tooltip_animation":1,"tooltip_container":"body","tooltip_delay":"0","tooltip_html":0,"tooltip_placement":"auto left","tooltip_selector":"","tooltip_trigger":"hover"},"user":{"uid":0,"permissionsHash":"e05d3e9aa272090c58ce9902a99e9f0a16b48e1778ec8cd3e516ef69bec1f87f"}}</script> <script src="/sites/default/files/js/js_w6lh8_Cmz0XvRlUKjMNZ-EFpA-rCBY1lfNSmyAa7tNs.js?scope=footer&delta=0&language=en&theme=cernclean&include=eJxdjFEOhCAMRC-E9kikQEPYVNqUanZvv6g_xq_JmzeZTNZjoSMOR98H5MnL5OXmsKHLJnBHOG3CQVBZEvIc_bj1evWZCftbJBEfbqigonKQPRoXYW8ashhBsV2R19KQpa74we91Gs9RQoMn_AHybkaa"></script> <script src="//framework.web.cern.ch/framework/3.0/js/prism/prism.js"></script> <script src="/sites/default/files/js/js_SgZcX5p6WViM80j8YfCfBiBJUek9xudHVE1eIj_yBmM.js?scope=footer&delta=2&language=en&theme=cernclean&include=eJxdjFEOhCAMRC-E9kikQEPYVNqUanZvv6g_xq_JmzeZTNZjoSMOR98H5MnL5OXmsKHLJnBHOG3CQVBZEvIc_bj1evWZCftbJBEfbqigonKQPRoXYW8ashhBsV2R19KQpa74we91Gs9RQoMn_AHybkaa"></script> <script src="//framework.web.cern.ch/framework/3.0/js/colorbox/jquery.colorbox-min.js"></script> <script src="//framework.web.cern.ch/framework/3.0/js/scroll-magic/ScrollMagic.min.js"></script> <script src="//framework.web.cern.ch/framework/3.0/js/scroll-magic/text-effects.js"></script> <script src="/sites/default/files/js/js_todlMQTOqUGUwgn2YnIhU1qk2zVKOeW8W59RbOJYtw4.js?scope=footer&delta=6&language=en&theme=cernclean&include=eJxdjFEOhCAMRC-E9kikQEPYVNqUanZvv6g_xq_JmzeZTNZjoSMOR98H5MnL5OXmsKHLJnBHOG3CQVBZEvIc_bj1evWZCftbJBEfbqigonKQPRoXYW8ashhBsV2R19KQpa74we91Gs9RQoMn_AHybkaa"></script> </body> </html>

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Tier centres | Worldwide LHC Computing Grid