Someone that worked set amazon at the time Glacier came out a while back commented that it is some type of extremely low power hard drive that backs this system

Someone that worked set amazon at the time Glacier came out a while back commented that it is some type of extremely low power hard drive that backs this system. Which makes sense due to the 1-4 hour delay in retrieval time. The racks are idle and only come online one every 4 hours or so and batch retrieve/store their data then power down. This small power usage is probably what makes them profit on this very slim margin.