Storage: an integral over time

Why is retention as strong a lever as size, and when does a colder tier pay?

Storage is an integral: money per byte per unit of time, added up for as long as the data exists. So retention is a lever as strong as compression. Halving the retention time halves the bill, just as halving the size does. Storage is also the only cost that grows while nobody is doing anything.

Tiering is a contract, not a medium

Tiering is usually taught as "colder media". That is often false. The tiers frequently run on the same hardware. The discount is a contractual construct: you accept (a) a retrieval charge, (b) a slower or less predictable latency and (c) a minimum billable duration. In return you get a lower storage rate.

Read it correctly and a cold tier is an option trade. You sell the vendor the option to charge you for reads and early deletes, and you collect a premium: the lower rate. The break-even is