When Does Fast Recovery Trump High Reliability?
نویسنده
چکیده
A widely accepted equation for availability is Availability=MTTF/(MTTF+MTTR), where MTTF is the mean time to failure of a system or subsystem (i.e. the reciprocal of reliability), MTTR is its mean time to recovery, and A is a number between 0 and 1. The equation suggests that to improve availability, a 10x decrease in MTTR (for example) is just as valuable as a 10x increase in MTTF, a founding observation of the Recovery-Oriented Computing (ROC) project [9]. In this paper, we argue that for interactive Internet applications, a decrease in MTTR is sometimes more valuable than the corresponding increase in MTTF to improve Availability by the same amount, and we make a case for adopting MTTR as the primary metric for reasoning about system availability and focusing designs on fast recovery.
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