I re-read the IOPS section i think you got part of that wrong a standard drive as it increases capacity its IOPS continues to drop. To combat this by splitting the drive in two it gives it a bump in IOPS to counter the penalties the increased capacity have been causing over the years.
This really at a high level is two 10TB drives sharing 1 housing and 1 sata port/power connection.
Edit: thinking about this further this is also where HDDs can potentially gain so real efficiencies. They are at 2 now but why stop there a 4 platter drive could potentially have 4 motors and 4 individual actuators to greatly increase speed without the price tag of a 10TB-20TB SSD.
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