Geo-Replication Calculator

shipped per day = primary × daily change rate × (1 − compression); sustained Mbps = shipped × regions × 8,000 ÷ 86,400; catch-up = backlog ÷ (link capacity − sustained rate). Replication traffic tracks the change rate, not the dataset size, so a 4 TB store that churns 4% a day ships about 160 GB before compression. Each additional replica multiplies both the storage bill and the egress, and the link only recovers from an outage using the capacity left above the steady change rate — which is why a link at 90% utilisation never catches up.

Sizing a replication link on average throughput guarantees permanent lag during the daily write peak, and lag is the same thing as data loss when the primary region fails. Inter-region transfer prices differ per region pair, so confirm the current rate with your provider.

This calculator takes 9 inputs: Primary dataset, Replica regions, Data changed per day, Compression achieved on the wire, Replica storage price, Inter-region transfer price, Replication link capacity, Change-rate peak factor, Replication outage to recover from. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.