For those of us who have been in IT for a while the term hierarchical storage management (HSM) has become more than a little old fashioned.
HSM was coined back in the bad old mainframe days when a high-capacity 300MB disk cost tens of thousands of dollars. At that time it made sense to have a primary array of disks backed up by a much slower, but far cheaper, tape library.
There are certainly some instances today where running an HSM system would appear to still make financial sense. Organisations such as the CSIRO in Australia, for example, are still heavily dependent on HSM.
Now cloud providers are coming of age and 200TB of consumer-grade disk can be had for as little as £20,000 (for the disks alone).