My quick TL;DR for other readers (please let me know if I'm wrong):

The systems described are servers that are over-provisioned with an order of magnitude more hard drives than you would typically see in a standard server. This allows a much higher ratio of total hard drive space to other components and cooling and power requirements, but at the cost of only being able to spin up some small fraction of the hard drives simultaneously. It then becomes a complicated scheduling problem of optimizing which hard drives to spin up and when based on the total workload of all the data you are trying to read and write at a given time. This system makes sense for data that is expected to be accessed on the order of once per year or less.

Yep. This is basically what they do. Source: I was around when they were designing and building Glacier.

This is very cool.

So Pelican fits 1152 WD WD6001F4PZ 6TB disks in 52U (Source: https://www.microsoft.com/en-us/research/video/rethinking-st...).

I wonder if microsoft going to publish specs (like opencompute?) to pelican servers?