If there's a userspace process that keeps the drive busy, running lsof /mnt/FileArchive while the partition is mounted should list it.
If the activity is internal to the mass storage driver, it could be due to filesystem error. Unmount the partition and check it manually with fsck.
On an unrelated note, you're setting fs_passno to 1 in fstab for no visible ...
I agree with @jow about that. I have had this problem before on my RasPi A+ too. Anyway, I tried to fix it by running
root@localhost# sudo e2fsck -vf /dev/sda1
too, although I got a "Non-existent file or directory" error with code 4092.
I eventually (after a month or so) fixed it with
root@localhost# sudo e2fsck -vf /run/mount
and that worked for ...
I have essentially the same setup except: two platter drives on a Rpi-3.
Take a look at the file "/etc/mtab". It is a "ln -S" link into /proc. The file shows how the disks were mounted exactly by the file system.
My two drives spin down when not in use. I use mine for network backups. When I login in takes about 30 seconds for the ...