Is it possible to use an 2.5" HDD (Internal HDD with enclosure) using USB 2.0 on Le Potato? For reference I’ll be using Toshiba which is 5V 1A rated. Can it be powered sufficiently over USB 2.0 interface or should I invest in an external powered hub? It’s worth noting that the only things connected to Le Potato will be this HDD and a fan (optional, or I’ll go for heatsinks instead).
This depends on your MicroUSB power supply. The USB ports can deliver 1A max and as long as the voltage does not drop below a certain threshold, you are OK.
HDD sometimes draw over 1A during startup and can cause brownouts. It is not recommended to power spinning HDDs directly but as long as your design is controlled and electrically coherent, it will work fine.
I have a Seagate 2TB external HDD that I use with my Le Potato, and the on-board USB were unable to power it. I had to get a powered USB hub to use the external HDD.