Sixns

Sixns, also known as six-nines or AT&T's reliability specification, is a term used to describe a level of system or network reliability where the system is available 99.9999% of the time. This level of availability is typically associated with redundant systems and high-quality hardware, as well as rigorous testing and maintenance procedures.

In the computing industry, a five-nines system would be considered extremely reliable, as it means that only a single failure would cause the system to be unavailable for less than one minute out of every 100,000 minutes. To achieve this level of reliability, system designers often implement multiple layers of redundancy, including backup power systems, network redundancy, and duplicate systems.

The term "six-nines" originated from AT&T's TUP (Trade/Joint Usability Plan) specification, which defined various levels of system reliability. Six-nines was considered an extremely high level of reliability, even among the highest standards of the time. Achieving six-nines reliability in production environments is extremely challenging, and many organizations do not attempt to meet this level of reliability.

While nine-nines may be rare in production, disaster recovery systems and testing environments are sometimes designed with this level of reliability in mind. These environments aim to simulate real-world conditions and high-stress scenarios, making them valuable testing tools for system administrators and developers.