Learn in the textbookReliability Metrics
DefinitionMTTR (mean time to repair) is the average time from the moment a failure stops the system until repair is finished and it runs again.
ExplanationIt is found by dividing the total time spent on repairs by the number of failures. A smaller value means faster recovery, so it serves as a gauge of the system's maintainability (保守性), meaning how easy it is to fix.
AnalogyIt is the average number of hours from getting a flat until the bike is fixed and you can ride it again.
Memory hookTo Repair in Mean Time To Repair means "until it is fixed", so it measures the time spent stopped.