Hi!
In Drive Management there is Idle option, mine is set for 900 seconds for external HDD. It works ok for first time (after applying), drive spins down, but later it stops working (after reboot for example) and drive is always spinning.
Please check that the settings have been applied and cmdline does not block hdparm init script:
cat /etc/hdparm.conf
cat /proc/cmdline
Which /dev/ name does the drive have? /dev/sda or similar?