But at 25kbps sustained write (inc optimistic disk juggling) it'd take 463 days to write 1TB. If that's your comparison number, you'd need to factor in 17 drive

But at 25kbps sustained write (inc optimistic disk juggling) it'd take 463 days to write 1TB. If that's your comparison number, you'd need to factor in 17 drives running in parallel to write 1tb in February. And a robot, or 6 people to handle disks. And 14m³ archive space. And double all that if you want redundancy. But the abacus beads could store rotational data. There's at least 8 bits of data there, more if you can put some time in. That's free real estate there.