Someone trying to optimize storage cost for the first time almost always makes the same mistake — they spread out the S3 storage-class price sheet and pick Glacier Deep Archive, which has the cheapest per-GB unit price. Then a month later they look at the bill and cost has actually gone up. They put frequently retrieved data into Deep Archive, and the retrieval costs and minimum-storage-duration penalties overwhelmed the storage savings. The essence of storage cost is that it's not a single storage unit price but a function in which several costs — storage, request, retrieval, transfer — sum differently depending on the access pattern