# Unplanned downtime


![left](./student-guide/diagram/28-Reasons-for-Unplanned-System-Unavailability-01-01.png)

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One of the real challenges in designing a high-availability solution is to examine and address all possible causes of downtime. It is important to consider the reasons for unplanned and planned downtime. The chart shown in the slide is a classification of unplanned failures, which are classified as software failures, hardware failures, human errors, and disasters.

Under each category heading, the possible causes of failures associated with that category are listed:

  Software failures include operating system, database, middleware, application, and network failures. Failure of any of these components can cause system failure.

  Hardware failures include system, peripheral, network, and power failures.

  Human error is the primary cause of failure, including operator, user, database administrator, or system administrator errors. Another human error that can lead to unplanned downtime is deliberate destruction.

  The last category is a disaster. Although uncommon, they can have an extreme impact on businesses due to their long-term impact on operations. Possible causes of disasters include fires, floods, earthquakes, power outages, and explosions. A well-designed high-availability solution takes all of these factors into account to prevent unplanned downtime.