After updating to 6.9 Final the HDD's (sata) no longer go into standby (after 30 min), no spin down.   I also set the delay to 15 minutes but the HDD's just don't go into standby. I have not changed any system settings before, only when I tried to solve the problem (uninstalled plugins etc.).   Before the update, on 6.8.3, the spin down worked fine.   I hope that you can help.  
Solved Minor