High Availability is the ability of a system to continue operating with a very high probability (probability of 99.999%), even if one of the system components fails. The goal, therefore, is not only to restore operations very quickly after a failure, but also to prevent the failure in the first place. The high availability is the highest of various availability classes that a system can have. Here it means that systems have a maximal uptime and minimal downtime with respect to the aforementioned level of reliability. The remaining availability classes have the same goal, but with slightly higher downtimes and a slightly lower level of reliability (e.g. reliability of 99.99% or 99.90%). Particularly in view of the high degree of technological advances and digitalization of today’s companies, the high availability of systems takes on significant importance.