I wanted to have my RAID5 array to go to standby after 10 minutes of inactivity. I achieved this with:
/sbin/hdparm -S120 /dev/sd[a-i]
But my drives were waking up from their standby because I had mythtv-backend configured with UPNP support.
To disable UPNP and thus scaning of video folder you have to edit /etc/init/mythtv-backend.conf
ARGS="--logfile /var/log/mythtv/mythbackend.log --user $USER --noupnp"
and add “–noupnp” at the end of ARGS line and restart mythtv-backend with “service mythtv-backend restart”.
Be sure that you are not running hddtemp as daemon and also that your recording folder is not on the RAID5 that you want to send to sleep. Not even symlinks on the RAID5 because it will wake up the disks when mythtv-backend runs auto expire scheduler searching for space to be freed.