HA vs FT vs DR

High availability (HA)

Aims to ensure an agreed level of operational performance (uptime). Systems can be unavailable only within agreed time borders. Maximising uptime. It’s like having a spare wheel.

Fault Tolerance (FT)

Systems must work after a fault occurs. Disruption prevention. Must work through failure without disruption. Involves HA, but requires more than that. It’s like a plane that has two pilots, two pilot seats, 4 engines, crew of multiple people. Highly available plane is disastrous, but fault tolerant plane isn’t.

Disaster Recovery (DR)

Set of policies, tools and procedures to enable recovery or continuation of vital technology in event of a disaster. Involves pre-planning, documentation, maximum knowledge availability between staff