Previously posted with write results only, now the graph below adds read speeds in green.
As explained in Reader Question: Drive Speed of 6TB vs 8TB Hard Drives, real world hard drive speed is primarly a function of capacity utilization.
In fact, capacity utilization dominates the performance equation and is thus the only realistic metric for transfer speed when real-world peformance considerations come into play. Other benchmarks are largely context-dropping irrelevancies. Moreover, if a drive is partitioned to use a volume on the fast part of the hard drive, seek time across that volume also drops (because the physical distance is tighter, the drive heads have less distance to travel).
The consistency seen is impressive: less than 2% variation among five samples across the entire capacity.
The 8TB HGST Ultrastar He8 declines in performance by nearly 50% as it reaches capacity, unusually poor in this regard. so how does it compare to its 6TB HGST Deskstar NAS sibling over the first 6TB of capacity?