Just two ideas:
Simil RAID-4 or RAID-5 architecture within platters drive to improve reliability of entire drive.
When one sector of “simil array” did fails, it can be reallocated without data loss.
Pro: more reliability, more read speed, relatively simple implementation with minumum of 3 heads/2 platters.
Cons: more complexity firmware and processor/controller , less amount of data avalaible, less write speed performance.
Single arm with two “L-shaped” or “Y-Shaped” head to minimize access time.
When the requested sector is in the first half of the drive , data was readed from “sub-head 1” otherwise from “sub-head 2”.
Pro: half average access time, relatively simply firmware implementation.
Cons: more head complexity and weight, solve problem with head parking.
Thanks & Bye