External USB disk sleep, CoreOS vs Fedora Server

Hello everyone! So, I was running a NAS at home using Fedora Server. The NAS uses two external USB disks, and they would never “sleep” (meaning they would not spin down when not used). I recently moved my server to CoreOS + Docker containers, using Jorge’s approach and I am super happy. However, with the same exact hardware, the disks now sleep when not used, and take a few seconds to come back when used. I would like to avoid this. Does anyone please know what could be keeping the disks awake with Fedora Server? I thought about hdparm, but it was not installed neither in Fedora Server nor in CoreOS. What could it be?