Compare cloud and local storage costs.
Cloud storage is a recurring cost that never stops, while a local drive is a capital cost repeated each time the hardware reaches end of life. Comparing them means projecting both over the same horizon and replacing the drive as often as its lifespan demands. The break-even month — drive price divided by monthly cloud spend — is the compact answer, and for bulk storage it usually arrives within a year or two.
Cloud and local totals
Cloud total = GB x price per GB per month x 12 x years; local total = drive cost x ceiling(years / drive lifespan)
Break-even
Break-even months = drive cost / (GB x cloud price per GB per month)
Not entirely. Cloud pricing includes offsite redundancy, durability guarantees and access from anywhere, none of which a single local drive provides. Comparing raw cost per gigabyte understates that.
The cloud side omits egress charges, which can be substantial on a full restore. The local side omits electricity, enclosure cost and the offsite copy you still need for real protection.