It's a great idea. It just doesn't work. HDDs don't have the right performance characteristics, unfortunately. You can do about 300 random access per second on

It's a great idea. It just doesn't work. HDDs don't have the right performance characteristics, unfortunately. You can do about 300 random access per second on a good HDD, which isn't enough to keep up with Ethereum's transaction rate, and each transaction needs quite a few of those each. You can do about 300,000 per second on NVMe. 1000 times faster. That's plenty.