Allegedly, on or about 7 December 2017, Fulko Hew sent:
hdparm -B 255 /dev/sda
But on this machine/drive, it doesn't seem to work;
or at least it only works for a short while, and then it starts
unloading again.
It sounds like it does work, but something else is changing the
settings on you later on.
I don't think you've said how long your change works for.
I don't recall you saying what desktop you use. It may help people
narrow down what might be periodically undoing your setting.
--
[tim@localhost ~]$ uname -rsvp
Linux 4.13.16-202.fc26.x86_64 #1 SMP Thu Nov 30 15:39:32 UTC 2017 x86_64
Boilerplate: All mail to my mailbox is automatically deleted.
There is no point trying to privately email me, I only get to see
the messages posted to the mailing list.
A positive attitude is worth the effort if it annoys enough people.