Booting grml from USB, we often turn IDE drives off:

# hdparm -Y /dev/hda /dev/hdb /dev/hdc

This works fine but causes "shutdown -h 0" to fail with "lost interrupt"
message.  Hard manual power off is necessary to shutdown.  Note that restart
still works ("shutdown -r 0").

There are no file systems mounted on the IDE drives when we turn them off,
that's not the issue here.