I do not own a Raspberry Pi yet so I could not test this but I plan to get a 40 watt 5 port USB charging hub and have that power the Pi and a 2.5 hard drive (HDD); yes in this scenario 3 ports of the hub go unused. I will also wire and code a power button to turn the Pi on and off.
In my use case the Pi will turn off (power down) but what about the HDD? If the HDD is directly connected to the USB power hub does it stay on all the time or does the pi send a shutdown signal and the HDD powers down as well?
If the hdd is always on in this use case how can I modify it to not be? Could I run 2 power cables to the pi (one to the pins and one to the normal power input) so the pi has enough power for the HDD but insures it goes off with the pi?
I will eventually use another device or hat to truly kill power to the pi. The power button will issue the halt/ shutdown command and then the extra device will kill the power. I fear this will leave the HDD running though unless I power it from the pi directly.