First, S3 is optimized for rapid retrieval (generally tens to hundreds of milliseconds per request). Glacier is not (we didn’t call it Glacier for nothing). With Glacier, your retrieval requests are queued up and honored at a somewhat leisurely pace. Your archive will be available for downloading in 3 to 5 hours. Secondly, S3 allows you to assign the name of your choice to each object. In order to keep costs as low as possible, Glacier will assign a unique id to each of your archives at upload time.