A few PCIe SSDs should get you there (again if not CPU bound). You can put quite a lot in a single machine, they come in normal SSD form factor with backplanes.

A few PCIe SSDs should get you there (again if not CPU bound). You can put quite a lot in a single machine, they come in normal SSD form factor with backplanes. It would still be a bit higher latency than RAM, but much more capacity.