Hi I have use my Bpi as NAS.I connect to It 3.5 hdd. And somtimes hdd restart spontaneously. I think this is because voltage drops. And I add two capasitor one for 12V and one for 5V.
[BPI-R64] Truble with HDD
to be honest powering 3.5in hdd from arm arm-board is a bad idea…
you should be powering it separately