“RAS” is the ability of the system to provide resilience starting from the underlying hardware all the way to the application software through three components collectively referred to as “RAS” features: ​
Reliability: the ability of the system to detect and correct faults​
Availability: how the system guarantees uninterrupted operation with minimal degradation
Serviceability: the ability of the system to proactively diagnose, repair, upgrade or replace components at scale​