If power provisioning and space are an issue it seems unlikely to me that they're sitting with many drives all hooked up for immediate power-up. It would make m

If power provisioning and space are an issue it seems unlikely to me that they're sitting with many drives all hooked up for immediate power-up. It would make more sense to separate the storage of media and the power connection so you get the most from each power connection. Therefore: removable media, whether those are hard drives or optical. There's a data retrieval period of multiple hours [1]. That doesn't sound like they're just powering up a drive. It sounds like they're moving something around or doing some kind of linear read (as opposed to random-access). I'd bet on "a retrieval job fetches this stack of read-only media and connects it to the powered device, which loads it onto hard drives for quick download". [1] "Retrieval jobs typically complete within 3-5 hours" - http://aws.amazon.com/glacier/faqs/ http://aws.amazon.com/glacier/faqs/