The author quickly dismisses hard drives because at the time of the Glacier launch SMR drives were to expensive because of the Thai flood. But after a few years of running S3 and EC2 Amazon must have tons of left-over hard drives which are now simply too old for a 24/7 service.
So what do you with those three year old 1 TB hard drives where the power-consumption-to-space ratio is not good enough anymore? Or can of course destroy them. Or you actually do build a disk drive robot, fill the disk with Glacier data, simply spin it down and store it away. Zero cost to buy the drives, zero cost for power-consumption. Then add a 3-4 hour retrieval delay to ensure that those old disk don't have to spin up more than 6-8 at times a day anymore even in the worst case.
So what do you with those three year old 1 TB hard drives where the power-consumption-to-space ratio is not good enough anymore? Or can of course destroy them. Or you actually do build a disk drive robot, fill the disk with Glacier data, simply spin it down and store it away. Zero cost to buy the drives, zero cost for power-consumption. Then add a 3-4 hour retrieval delay to ensure that those old disk don't have to spin up more than 6-8 at times a day anymore even in the worst case.
But that's just my personal theory anyway.