Diodato

The only way I was able to get the drives enter sleep was to de-install DrivePool and Scanner, since it wasn't my main PC setup.

Hello again Christopher,
On the machine in question only DrivePool and Scanner are installed. I have CloudDrive but I use it on a different PC on a different LAN.
I have verified thrice just to be sure and here is my setup and observations:
- PC setup: Win10 1909 build 18363.815, DrivePool version is 2.2.3.1019 , Scanner version is 2.5.6.3336
- Three USB disks attached (drive letters D, E and F) (TerraMaster D5-300C enclosure)
- Scanner has under SMART throttling set to 60 minutes, "only query during the work window or if scanning" set and "do not query if the disk has spun down" also is set.
- DrivePool is not configured for any pool disk, as if just installed. DrivePool has "BitLocker_PoolPartUnlockDetect" set to "false" (both Default and Override)
- the DrivePool Service is Stopped
- the active power plan of Windows has disk spindown set to 3 minutes. All three disks are not spinning.
- Procmon64 shows abolutely no processes accessing the D, E or F disks
- Resmon (disk tab) shows absolutely no activity for disks D, E and F
Now as soon as I enable the DrivePool Service the disks wake up and never again go to sleep. You can see in the Resmon that every second there is access to all three disks. In the image in my previous post accesses to disk D are obvious, but if look with attention, every second there are very subtle marks also for disks E and F (very small peaks). Procmon continues to show that nothing is accessing disks D, E and F.
If I stop the DrivePool Service I stop seeing in Resmon disk access for these three disks and after three minutes (whatever is set in the power plan) the go to sleep.
Once again if I restart the DrivePool Service the disks wake-up and I start seeing the same every second disk access activity in Resmon. Again the disks will never spin-down. Not until I stop the DrivePool Service.
 
Now I do not want to say that the DrivePool service is the culprit but it took me a very long time to narrow down what is causing my external USB drives not to sleep. Because Procmon was useless (no process was accessing the disks) I started stopping different services and have observed the above described behavior with the DrivePool Service.
As the authors of DrivePool I am kindly asking for suggestions what to do to have my external disks spin-down or how to continue investigating. It might be a Microsoft Windows or USB driver problem or other but I would like some help or directions with the next steps. Thanks in advance. Cheers.