Thanks, I know that the post is old but I have the problem. Did try both methods. The ac adapter is 5V 2 amps. The external hdd is the ‘western digital my ultra passport’. The raspberry pi 2. The external hdd starts clicking and the osmc freezes.
Just because you have set max_usb_current=1 doesn’t mean that your Pi is guaranteed to power all external 2.5" hard drives - many drives simply draw too much power regardless of this setting.
Also, just because your power adaptor may state 5v 2 amp on the label doesn’t mean that it maintains 5 volts under a load of 2 amps - a large percentage of micro USB adaptors do not as they are only designed as chargers not power supplies. So unless your adaptor is specifically made for the Raspberry Pi, there is no guarantee that the voltage is staying at 5v with the extra load of the drive.
You could try a different power adaptor but if that doesn’t work your only choice is to power the hard drive with it’s own power adaptor.