hd-idle is a [Linux] utility program for spinning-down external disks after a period of idle time.
hdparm -S won't work for WD drive. So I found this great alternative. This is a great disk idle utility for western digital hard drives in linux. Very easy to use and put my hard drives in standby mode after 10 min inactivity. My OS is debian, I create a soft link in /etc/init.d and use update-rc.d to start hd-idle on boot. Works great.
Thanks for Hd-idle, it's perfect!
What a great way to save the spindle bearings on my external hard-drives, for basically zero system resources!