On Librem Mini, is it possible to make a setting in coreboot such that USB ports are unpowered when PC is off? Currently, my external HDDs have the LED on and keep spinning even when the device is off.
Is it a correct assumption that the boot drive is internal? In that case, is it a possibility to use
hdparm.conf to spin down the external drives when not in use, after X seconds - regardless of whether the Mini itself is up or down?
No, neither coreboot nor the EC can control this on Mini. I agree with the
hdparm suggestion, that’s where I would look. Depending on your workload, you could have the disk spin down any time it idles for a configured time, or you could do it when the host is shutting down.