The Free On-line Dictionary of Computing (30 December 2018):

Reliability, Availability, Serviceability

    (RAS) Three key attributes
   of a computing system design.  See reliability, availability,
   and serviceability.

   The term "RAS" is fairly common in the computing industry
   (particularly computers and storage) as computing becomes more
   fundamental.  For example, a vehicle may depend on dozens of
   computers, and the consequences of the failure can be
   significant (e.g., an ambulance's engine won't start).

   (2000-08-13)