I finally managed to spin down my external USB-drive. I post it here
in case someone is interested in this:
I run Debian and have an external USB-drive for data. I tried to spin
it down using the techniques proposed on the wiki-page, but none of
them seemed to work for me. I came across the tool hub-ctrl
, which allows you to
cut the power to the drive on the usb-hub. You can compile it using
"gcc -o hub-ctrl hub-ctrl.c -lusb"
I can make my device spin down by "hub-ctrl -P 2" (it's attached to
the second port) and start it again by "hub-ctrl -P 2 -p 1". Take care
that you don't power off the port which holds your root partition. It
will make your system unresponsive.