On occasion, I have to build custom storage servers for my data center. They are usually for archive data that doesn't get accessed that often, but retention requirements make it so the data must be around for 10 years.
Just out of curiosity, have you considered tape or optical media for a nearline or offline storage solution?
That is how medical images used to be archived. While the media is cheap, the size of the autoloader needed is insanely expensive. Tape media is also a pain to track, and isn't the most reliable when you actually need to recover data. I haven't used tape in any form since about 2008 and I am okay with that. The data also needs to be readily available for two years or so, as the applications can call on the data at any time until the pointers are purged from the database. It is a complicated mess, but I have implemented a cost-effective solution for the needs of the company.