/dev/sda:
setting standby to 200 (16 minutes + 40 seconds)
#hdd status
hdparm -C /dev/sda
#config file
cat /etc/hdparm.conf
hdparm -B 1 -Y /dev/device
hdparm -B 255 /dev/device
The first hdparm put the device standby immediately. The second one turn off APM, so the disk stay in standby mode till the next disk access.