Hello @seeeder,
First of all, you can only connect a maximum of 2 HDDs to the board with a power supply of 12V/3A directly connected to the board. The included power supply in the box is 12V/2A. So, with that, you can only connect a maximum of 1 HDD. This is the limitation from the board. If you want to connect more than 2 HDDs to the ODYSSEY board, you need to power the HDDs separately. This is because the HDDs will not have enough power just by powering up the board using a 12V/3A power adapter.
You need a power supply like this to power the HDDs separately:
You need a power supply as above because HDDs need both 12V and 5V to function.
Also, you could use these cables to connect the HDDs to the above-mentioned power supply:
Hope it helps.
Best Regards,
Lakshantha