Huawei Ascend P6 Quick Start - Manual (Page 69)

Sharing data
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Do not remove a storage device from your phone before unmounting;
otherwise, data may become corrupted. To unmount the external device,
touch on the home screen. Then touch All > Storage > Unmount USB
storage to unmount the USB device.
Your phone supplies power to USB storage devices. Certain phone models
and mobile hard drives have relatively high rates of power consumption,
meaning your phone may not be able to supply enough power for them to
run properly.