Glossary
Also: Recovery Time Objective · Recovery Point Objective
Two numbers for the bad day: how long recovery may take (RTO), and how much data may be lost in the process (RPO).
Both are business decisions, not technical ones. An hour of downtime costs something entirely different in an online shop than in an internal tool, and that determines how much protection is worth building.
Architecture follows from RTO and RPO, not the other way round: an RPO of zero means synchronous replication, and with it latency and cost. An RPO of four hours allows a simple backup procedure.
How you notice it
Frequently asked
From the cost of downtime, not from technology. Work out what an hour of standstill costs in revenue, penalties and rework. Only that number makes the question decidable whether synchronous replication is worth its price or an hourly backup suffices.