Disaster Recovery (RPO vs RTO).

RPO (Recovery Point Objective) and RTO (Recovery Time Objective) define disaster recovery targets.

RPO dictates acceptable data loss. An RPO of 1 hour means you must back up data at least every hour; in a crash, you lose up to 1 hour of transactions. RTO dictates acceptable downtime. An RTO of 4 hours means the system must be restored and functional within 4 hours of the disaster. Tighter RPO/RTO requires active-active architectures and continuous replication.