Adding Spindown to Drives – Changing system settings?

Hello,

I plan on letting my Pi2 constantly on in the future, but the problem is that there are two usb harddrives connected. Apparently they do not spin down if idle for a given time. I tried it on the ssh terminal, and I can do it with hdparam, so I would like to add this. For this I need an hdparam.conf in /etc/, but as you all know, kodi is read only. I read that in order to add this, I would need to basically open the image with squashfs, but when I try this it always says “Can’t find a SQUASHFS superblock on kodi.img”. I tried it with /dev/sdf, /dev/sdf1 and /dev/sdf2, none of them work and yes it is the correct device.

So how I can achieve my goal?

Thx.