Comparison
Data downtimevsMean time to restore
Data downtime
the numbers were wrong from Tuesday 02:00 until someone noticed on Thursday afternoon, and that gap is the thing worth measuring.
The period during which data was missing, wrong or stale, measured from when it broke to when it was fixed. Naming it as downtime is the useful move: it makes detection time visible as a separate number from repair time, and detection time in data teams is routinely measured in days. Almost every investment in quality checks is an argument about reducing the first number.
Full entry →Mean time to restore
the outage started at 09:14 and traffic was healthy again at 09:31, and that number is the one that got tracked.
How long it takes to restore service after a failure in production. It matters more than the failure rate for most systems, because failures are inevitable and duration is the part you can engineer: rollback speed, observability, a rehearsed on-call. Optimising for it changes design decisions, since a system that can be restored in minutes can accept risks that one requiring a four-hour restore cannot.
Full entry →