Your everyday modern HDD does not much more than 60MB/s after the on-disk cache (a few GB) is full.
not sure what you’re on about, i have some cheap 500GB USB 3 drives from like 2016 lying around and even those can happily deal with sustained writes over 130MB/s.
When the cache isn’t full, yes, that’s true. Copy a file that’s significantly bigger than cache and performance will drop part way through.
You’ve made me uncertain if I’ve somehow never noticed this before, so I gave it a shot. I’ve been dd-ing /dev/random onto one of those drives for the last 20 minutes and the transfer rate has only dropped by about 4MB/s since I started, which is about the kind of slowdown I would expect as the drive head gets closer to the center of the platter.
EDIT: I’ve now been doing 1.2GB/s onto an 8 drive RAID0 (8x 600GB 15k SAS Seagates) for over 10 minutes with no noticable slowdown. That comes out to 150MB/s per drive, and these drives are from 2014 or 2015. If you’re only getting 60MB/s on a modern non-SMR HDD, especially something as dense as an 18TB drive, you’ve either configured something wrong or your hardware is broken.
