Which is the cheapest S3 storage class?

The deep archive is the back room of the building. Nothing in it can be opened directly. You ask for a file, wait up to twelve hours (or up to two days on the cheapest option), then read a temporary copy.

The shelves, cheapest first

$1.01a month per TB

Glacier Deep Archive: six-month minimum, hours to get a file back

$3.69a month per TB

Glacier Flexible Retrieval: 90-day minimum, minutes to hours to get a file back

$4.10a month per TB

Glacier Instant Retrieval: 90-day minimum, opens instantly, $0.03 per GB read

$12.80a month per TB

Standard-IA, the rarely-opened shelf: 30-day minimum, $0.01 per GB read

$23.55a month per TB

S3 Standard, the normal shelf: no minimum, no fee to read

Two catches on every cheaper shelf

• Every file is charged for its minimum stay, even if you delete it the next day.
• Files under 128 KB are billed as if they were 128 KB, so a bucket of thousands of tiny documents saves less than the rate suggests.

For files people still open now and then, Glacier Instant Retrieval is the sweet spot: a sixth of the normal rent, and the file opens at once.