As per the title, I recently bought a Raspberry Pi 2 Model B and I thought it would be nice to have some extra space so I plugged my external HDD.
Here's the specs:
The power supply: CSL - microUSB Netzteil / Ladegerät (2100mA / 1000mA) | 5V DC USB
The OS: Raspbian
I would like to mention, that the Raspberry Pi works marvelously, powering the HDD is the only problem.
The HDD works well, on both 3.0 and 2.0 USB ports, on my laptop, desktop, TV, PS3, Wii.
Whilst on the Raspberry Pi, it spins for a few moments then stops, it alternates like this for as long as it's connected.