Storage Replication Cost Calculator (S3 CRR/SRR and Cross-Region Copy)

What this replication calculator is best for

This page is most useful when you need to separate steady changed-data replication from one-time copy bursts. It is built for teams planning S3 CRR, SRR, cross-region copy, or DR replication and trying to avoid the classic mistake of modeling the whole dataset instead of the data that actually moves each month.

• Ongoing replication: changed GB per month in normal operation.
• Backfills and migrations: one-time spikes that should not pollute your steady-state baseline.
• S3 CRR vs SRR planning: comparing same-region and cross-region copy assumptions.

Changed GB, not total stored GB, is the main driver

The most common replication mistake is using total dataset size instead of the data that actually changes and gets copied. For ongoing replication, write volume and churn are usually the correct drivers.

• Measure writes first: estimate changed GB from write throughput, sync batch size, or daily churn.
• Separate event types: keep ongoing replication, one-time backfills, and DR drills in different scenarios.
• Match billing direction: confirm whether your provider bills source-to-destination copy, feature fees, or both.

SRR, CRR, and billing boundaries

• Same-region replication: often more about feature overhead and extra storage than internet-style transfer.
• Cross-region replication: usually needs explicit transfer assumptions and stronger peak modeling.
• DR planning: add drill, failover, and catch-up windows as separate scenarios instead of inflating the baseline.
• Replica storage: keep storage in the destination region separate from the replication-transfer line.
• Requests and retries: high-write workloads may create adjacent request charges that deserve their own estimate.

The estimate becomes much cleaner when you keep three things separate: changed GB that is copied, storage that accumulates in the replica location, and one-time backfill or migration activity. Mixing those together is how a normal month starts looking far more expensive than it really is.

Scenario planning and first-bill validation

• Reconcile steady-state changed GB against observed writes, not total dataset growth.
• Keep one-time backfill costs out of the recurring monthly baseline after the migration is finished.
• Check whether replica storage growth or request amplification explains the remaining gap before changing the transfer rate.
• DR readiness: steady changed GB with occasional test-failover spikes.
• Migration: short-lived, very high replicated GB and transfer bursts.
• Multi-region reads: steady replication plus possible egress from secondary reads.
• Compliance archive: low change rate but long retention and storage growth.

A good validation rule is simple: if a spike comes from a migration, DR drill, or backlog catch-up, it belongs in a separate peak scenario, not in the steady-state replication baseline.

Billing checklist and common failure patterns

• Replication transfer fee and replica storage fee are modeled separately.
• One-time backfill is not merged into steady monthly change volume.
• Request amplification from replication is captured for high-write workloads.
• Directionality (source to destination) matches provider billing rules.
• Using total dataset size instead of changed data volume is treated as a modeling error, not a peak assumption.
• Replica-region storage growth after policy changes is checked separately from copy traffic.
• DR drill traffic is kept in a test scenario instead of becoming the default monthly baseline.
• Write amplification from retries, retries after failures, or small-object churn is reviewed before sign-off.

The most expensive modeling mistake is not usually the transfer rate. It is choosing the wrong driver: full dataset size, mixed-in backfills, or missing replica storage growth.

Next actions after the first estimate