Size a grandfather-father-son backup footprint from change rate and retention, split across warm and cold storage.
Incremental-forever backup stores one full copy plus the changed blocks behind every retained recovery point, so the footprint is driven by change rate and retention depth rather than by the size of the source. Long-retention monthly points each anchor a month of change, which is why they usually dominate the total even though they are the fewest in number, and why they belong in cold storage. Both prices are user-supplied list prices to confirm on the AWS Backup pricing page for your region. It explains the recurring surprise that protecting 2 TB needs closer to 18 TB of backup storage, and shows that trimming monthly retention moves the bill far more than trimming daily retention.
Backup Storage
footprint = full copy + Σ(recovery points x days covered x daily delta x unique-block factor), where daily delta = primary GB x change rate.
footprint = full copy + Σ(recovery points x days covered x daily delta x unique-block factor), where daily delta = primary GB x change rate. Incremental-forever backup stores one full copy plus the changed blocks behind every retained recovery point, so the footprint is driven by change rate and retention depth rather than by the size of the source. Long-retention monthly points each anchor a month of change, which is why they usually dominate the total even though they are the fewest in number, and why they belong in cold storage. Both prices are user-supplied list prices to confirm on the AWS Backup pricing page for your region.
It explains the recurring surprise that protecting 2 TB needs closer to 18 TB of backup storage, and shows that trimming monthly retention moves the bill far more than trimming daily retention.
This calculator takes 8 inputs: Primary data protected, Daily change rate, Share of changed blocks that change again, Daily recovery points kept, Weekly recovery points kept, Monthly recovery points kept, Warm backup storage price, Cold backup storage price. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.
Each daily point only carries one day of change, while each monthly point carries about thirty. Dropping one monthly point removes as much storage as dropping thirty daily ones.