@Cremejoghurt Welcome to the Rockstor comunity forum.
Rockstor doesn’t really do a sleep mode but I can have a quick go at the hdd power down / wake on request config:
If you visit the Storage - Disks page and click on the hour glass icon:
In the above image I have only configured the second drive to show the difference.
Do this for each of the drives you wish to spin down automatically.
The configuration screen along with relevant instructions:
And with both drives configured:
And after about 10 mins in this case we have:
Note however that accessing the Plex UI will wake up and possible keep awake the drives used in it’s pool. Also note that if you have the Plex sever library option “Update my library automatically” enabled then it will wake your pool drives every 15-20 minutes so this must be disabled to enable the drives to remain in standby. Another caveate is that ‘watching’ the drives by having the Disk page open may also prevent the drives from entering their spun down ‘standby’ state.
This option is found within the plex ‘tools’ menu then the ‘Server’ tab, then the Library section.
We do have a pending documentation issue which I will have a go at soon and possibly use these existing images for that purpose:
Hope that helps.