What is MTTR and MTTD and why do they matter to SRE teams?

MTTR (Mean Time To Recover) and MTTD (Mean Time To Detect) are reliability engineering metrics that quantify two key phases of an incident lifecycle.

MTTD — Mean Time To Detect is the average time between when a failure actually begins and when the monitoring system (or a customer) first detects it. A low MTTD means your alerting and observability systems are working well — issues are caught quickly, before they impact many users or accumulate large error budget burns.

MTTR — Mean Time To Recover is the average time from detection to full service restoration. MTTR encompasses diagnosis time (finding the root cause), mitigation time (deploying a fix or rollback), and verification time (confirming recovery). A low MTTR reflects good runbooks, good observability (fast diagnosis), fast deployment pipelines, and practiced incident response processes.

These metrics directly reflect observability maturity. If MTTD is high, alerts are too slow or missing entirely. If MTTR is high despite fast detection, either the debugging experience is poor (missing traces or logs), deployments are slow, or on-call engineers lack the knowledge to diagnose the system. Observability improvements — better traces, correlated logs, runbooks linked from alerts — directly reduce MTTR.

DORA (DevOps Research and Assessment) research identifies MTTR as one of four key metrics for elite engineering organizations, alongside deployment frequency, lead time, and change failure rate.

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