Size per dingus is somewhat irrelevant to the use case: what's it matter if you buy 10 things that take up a rack or 20 things that take up a rack - how much di

Size per dingus is somewhat irrelevant to the use case: what's it matter if you buy 10 things that take up a rack or 20 things that take up a rack - how much did it cost to store all of your data at the speed you needed? Modern tape still has extremely good $/TB. If you have a LOT (and I don't just mean a fews 100s of TB) of data you need to keep but don't need to be able to access all of it constantly then tape can still save you a metric boatload of money on TCO vs SSD or HDD. Dual tier systems are for when a small amount of that data may be hot at any given time (like you say, financial often has a lot of active data in a pool of tons of inactive data they can't throw out. Medical is another example). Rather than manual manage this you just run a 2 tier system that automatically bumps things in and out of high $$$, high performance storage banks to low $, high capacity storage banks transparently.