I was thinking whether it makes sense to by default spin-down the
harddisks, e.g. via hdparm -y /dev/sdX or hdparm -Y /dev/sdX
That would have the advantage of reduced power consumption, less noise
(up to complete silence when the fan is not spinning), and proof to the
user that Tails is not accessing the HDD. Of course, the HDD need to
spin-up again if the user mounts it.
but what I cannot comment on is whether there may also be difficulties
from spinning-down the HDD (hardware failure? ...)