@heiner: ‚Raspberry‘ got me in – but I downloaded a fresh image from the website just last week – the version with touchscreen ?
I managed to find „#HD_IDLE_OPTS=“-i 180 -l /var/log/hd-idle.log“ via the consol – My hdd is sleeping now. I am not sure whether tinkering or rebooting helped, since I didn’t change any settings – I don’t know how 🙂
@teetertank: I am pretty sure that my HDD spinned down with a previous image – so it shouldn’t be a hardware issue.
Anyway, problem solved, it seems. Thank you for the answers and help.