High availability is a systems design approach that attempts to maximize the likelihood that a service or system will be available for end user usage. The Sisyphean goal of any such system would be to make the services and systems always available. Some very well-crafted designs promise what is commonly known as five 9s, which is guaranteed 99.999 percent availability. The percentage is tied to a specific length of time, typically one year. In order for a system to meet a five 9s standard, it must be unavailable for no more than about five minutes in an entire year's time.