Comments
A few factual inaccuracies in here that don't affect the general thrust. For example, the claim that S3 uses a 5:9 sharding scheme. In fact they use many different sharding schemes, and iirc 5:9 isn't one of them.
The main reason being that a ratio of 1.8 physical bytes to 1 logical byte is awful for HDD costs. You can get that down significantly, and you get wider parallelism and better availability guarantees to boot (consider: if a whole AZ goes down, how many shards can you lose before an object is unavailable for GET?).
I enjoyed this article but I think the answer to the headline is obvious: parallelism
By pjdesno 2025-09-2421:25 Note that you can kind of infer that S3 is still using hard drives for their basic service by looking at pricing and calculating the IOPS rate that doubles the cost per GB per month.
S3 GET and PUT requests are sufficiently expensive that AWS can afford to let disk space sit idle to satisfy high-performance tenants, but not a lot more expensive than that.
