In my very limited experience with my 5400rpm SMR WD disk, it’s perfectly capable of writing at over 100 MB/s until its cache runs out, then it pretty much dies until it has time to properly write the data, rinse and repeat.
40 MB/s sustained is weird (but maybe it’s just a different firmware? I think my disk was able to actually sustain 60 MB/s for a few hours when I limited the write speed, 40 could be a conservative setting that doesn’t even slowly fill the cache)
Not familiar with the API, and I’m not entirely sure if it’s not just a bug in Eternity (fork of Infinity), but lemmy.one doesn’t have downvotes and I don’t get the option to downvote anywhere.