MTTD and MTTA (time to detect and acknowledge)
MTTD is the average time from a failure starting to someone or something noticing it; MTTA is the time from the alert to a person taking it on.
They split MTTR into its parts. Long detection means you learn about problems from customers; the fix is better signals such as the four golden signals and error tracking that records every failure. Long acknowledgment means alerts go to a channel nobody watches, or there are so many that people ignore them; the fix is a clear on-call rotation and fewer, better alerts. Repair time is often the smallest part.
Related terms
- MTTR (mean time to recovery): The average time from a production failure to the service working again for users; one of the DORA metrics of software delivery.
- On-call rotation: A schedule that names who responds to production alerts outside normal work, with an escalation path if that person does not answer.
- Four golden signals (latency, traffic, errors, saturation): Four metrics from Google’s SRE book that cover most of what to watch on a user-facing service: latency, traffic, errors and saturation.
- Observability (o11y): Being able to tell what a running system is doing, and why, from the data it emits: logs, metrics and traces.
