I am able to spindown my SATA HDDs by using
sudo hdparm -y /dev/sdc
The state shown by
sudo hdparm -C /dev/sdc
changes from active/idle to standby (and I can hear the HDD spin down).
sudo hdparm -S5 /dev/sdc
doesn't spin down the drive after 5*5 = 25secs.
Some additional information:
- AHCI is enabled.
- I am using Western Digital Green drives.
- APM_level = not supported
- Filesystem is ext4