So I got this WD Elements 4TB external drive, that was an Amazon Warehouse Deal (I wanted a new one, this used one arrived, they already refunded). I decided to give it a go, but it has its problems, such as randomly lowered speeds on the area that's not free space. I've never seen anything like this. The test is conducted in Safe Mode Windows 10, nothing is accessing the drive. SMART data is healthy, there are no errors or bad sectors anywhere.
Earlier screenshot (see below) shows that when I used like 800GB, the random spikes stopped at ~800 and the standard downward curve started at that point. As I added more data, the graph changed, and the weird part grew in accordance with the used space. You can see that the pattern is the same, so it's not random.
