USB Harddisk. Always a mystery to me.

I found out a strange thing today: I have to plug both of the powered harddisk (Look A6 OTG harddisk and the old SamSung 80Gb hard disk) to the USB 2.0 Hub instead of directly connect to the USB port extended from the motherboard. Once again, using USB harddisk is all about trial and error. Sigh.