This is a useful and interesting contribution from Google. However, like a lot of current software and web-scale systems research, almost no attention is paid

This is a useful and interesting contribution from Google. However, like a lot of current software and web-scale systems research, almost no attention is paid to contributions from other industries, or even current practice in automotive, aerospace, consumer or finance, to name a few. The earliest reference in the paper is 1986, with most post-2001. A definition of availability is attributed to Toeroe and Tam 2012. It was most definitely in use decades before! The authors and interested others would benefit from reviewing current systems engineering practice (see INCOSE.org organization). Texts such as Blanchard and Blyler, Systems Engineering Management Blanchard and Fabrycky, Systems Engineering Analysis NASA, Systems Engineering Handbook (and accompanying management handbook) and others would open a few eyes, I expect. The biggest issue with the term "availability" for a single-instance system is well identified by Google. The term was originated, however, for many thousands-instances systems, such as procurement of combat aircraft, operating vehicle fleets and so on. Substituting another measure (and term) is a benefit. However, one issue I didn't see addressed in the paper: how to measure success for the purpose of an SLA. Contracts would need a simple comparison to a single number.