{"id":2637,"date":"2021-10-21T16:29:18","date_gmt":"2021-10-21T14:29:18","guid":{"rendered":"https:\/\/ur4-tia.com\/cyber-security\/high-availability-definition-classes-and-implementation\/"},"modified":"2022-03-02T16:04:01","modified_gmt":"2022-03-02T15:04:01","slug":"high-availability-definition-classes-and-implementation","status":"publish","type":"page","link":"https:\/\/ur4-tia.com\/en\/guide-information\/cyber-security\/high-availability-definition-classes-and-implementation\/","title":{"rendered":"High availability: definition, classes and implementation"},"content":{"rendered":"\t\t
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Definition of high availability<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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\n\t\t\t\t\t\t\t\t\tHigh availability<\/strong>\u00a0includes a set of technologies, procedures and design principles that support the goal of business continuity.\u00a0For systems or services, the goal of high availability means a defined, maximum tolerated downtime of generally 0.01%.\u00a0In other words: 99.99% availability is considered to be highly available.\r\n\r\nIdeally, systems and services are 100% available, i.e. accessible at any time during the agreed operating hours. However, this is rarely realistic and can only be mapped with enormous effort. For this reason, companies in many areas accept defined, maximum downtimes to keep the costs for services within realistic ranges.\r\n\r\nIn the operational environment,\u00a0availability<\/strong>\u00a0requirements are often agreed in the form of service level agreements.\u00a0The operating time is usually defined as a basis (e.g. 7\u00d724, i.e. around the clock, or Monday to Friday on weekdays from 8 a.m. to 4 p.m., i.e. 5\u00d78), with planned downtimes (e.g. maintenance windows) being included with exception of.\u00a0In addition to the operating time, the minimum percentage of the time that the system or the service should be accessible (uptime) is defined, e.g. this 99.99% as high availability.\r\n\r\nSuch specifications are intended to ensure that all components required for business operations can be used with a sufficiently high degree of probability during business hours.\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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availability classes<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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\n\t\t\t\t\t\t\t\t\tIn practice, in addition to percentage specifications and measurements, the\u00a0availability classes of the Harvard Research Group<\/strong>, the Availability Environment Classification (AEC)\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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AEC class<\/div><\/div><\/div><\/th>
Explanation<\/div><\/div><\/div><\/th><\/tr><\/thead>\n\t\t\t\t\t\t\t\t
AEC-0 \/ Conventional<\/div><\/div><\/div><\/td>
Service can be interrupted, data integrity not essential\r\neg: systems that do not store productive data, are not critical to business operations. In many SAP environments, for example, sandbox systems<\/div><\/div><\/div><\/td><\/tr>
AEC-1 \/ Highly Reliable<\/div><\/div><\/div><\/td>
Service can be interrupted, but data integrity must be guaranteed Service can be interrupted, but data integrity must be guaranteed\r\ne.g. systems that are not involved in productive processes but whose function can have an indirect\/medium-term impact on them. In the SAP environment, it is often the regular development and QA systems, since dependent data structures and test cases are mapped in these, or BW\/BI systems.\r\n<\/div><\/div><\/div><\/td><\/tr>
AEC-2 \/ High Availability<\/div><\/div><\/div><\/td>
Service may only be interrupted minimally during agreed times or during main operating hours,\r\neg systems that are critical during the productive times of a business process. In SAP environments, these are often the productive systems<\/div><\/div><\/div><\/td><\/tr>
AEC-3 \/ Fault Resilient<\/div><\/div><\/div><\/td>
Service must be maintained uninterrupted during agreed times or during peak hours of operation,\r\neg systems whose processes and data are absolutely critical to the business process. In SAP environments, for example, these are often the systems in the warehouse management environment, especially for chaotic warehouses, since a failure here would often lead to a full inventory<\/div><\/div><\/div><\/td><\/tr>
AEC-4 \/ Fault Tolerant<\/div><\/div><\/div><\/td>
Service must be maintained uninterrupted, 24\/7 operation (24 hours a day, 7 days a week) must be guaranteed As above, but with no restriction on uptime. This often includes systems for online services, where customers can quickly switch to alternatives, or KRITIS environments.<\/div><\/div><\/div><\/td><\/tr>
AEC-5 \/ Disaster Tolerant<\/div><\/div><\/div><\/td>
Service must be available under all circumstances Systems where life and limb are at stake, often in a critical environment, e.g.\r\nin nuclear power plant environments, etc.\r\n<\/div><\/div><\/div><\/td><\/tr><\/tbody>\n\t\t\t<\/table>\n\t\t<\/div>\n\n\t\t<\/div>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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\n\t\t\t\t\t\t\t\t\tTable 1: Availability classes according to AEC\r\n\r\nSource: Harvard Research Group,\u00a0https:\/\/hrgresearch.com\/High%20Availability.html<\/a>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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\n\t\t\t\t\t\t\t\t\tIn addition, there are other classifications, such as the BSI availability classes commonly used in Germany:\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t\"Availability\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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\n\t\t\t\t\t\t\t\t\tFigure 1: Availability classes according to BSI\r\n\r\nSource: Bundesamt f\u00fcr Sicherheit in der Informaionstechnologie, HV-Kompendium, Band G, Kapitel 2: https:\/\/www.bsi.bund.de\/SharedDocs\/Downloads\/DE\/BSI\/Hochverfuegbarkeit\/BandG\/G2_Definitionen.html<\/a>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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Calculation of high availability<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t
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\n\t\t\t\t\t\t\t\t\tAvailability is usually given as a percentage.\u00a0In general, the availability – and thus also the high availability – is calculated by dividing the uninterrupted service time of a service by the total (agreed) operating time.\r\n\r\nRegular maintenance windows, which are also explicitly regulated as planned downtimes in SLAs, do not count towards the service time.\r\n\r\n100% availability<\/strong>\u00a0means uninterrupted operation during the agreed service period.\u00a0With a 7\u00d724 operation, the typical \u201c9s\u201d mean the following maximum downtimes:\r\n