I have a Raspberry Pi 2 Model B and a 2,5 inch HDD that I want to connect via USB. The HDD also powers itself over USB. Does the Raspberry Pi 2 Model B provide enough power? Can I safely run the HDD without breaking any of the two devices?
You SHOULD be able to power a HDD from the Pi2 (provided you use an adequate power supply AND set
max_usb_current=1). The max USB current is 600/1200mA depending on
Unfortunately adequate power supplies are not common. See the comments in https://raspberrypi.stackexchange.com/a/47642/8697 Even though this is Pi3 the issues are the same and the power circuitry very similar.
No, it does not! You can harm your RPi board seriously if you will power your HDD from it, even attaching a 5Amp PSU : the RPi board is simply not designed for such currents. Use a USB hub with external PSU and it will be OK, or - if you're about to use just a one more PSU for your HDD, make sure you've connected it's GND(Ground) with the one supplied to RPi