Booting from USB on Pi3

[ZXSpectrum]

Hi Guys, Is there a program I can use so that I can boot from a MicroSD card on the PI but then have a HDD or USB Key plugged in that has a big image on it with the OS/Media?

I thought Raspberry Pi Maker would work but apparently that's mainly for multiple OS on one SD card.

Any help would be appreciated.

 

[Feek]

The first steps on this guide do exactly what you want. I've done this and my Pi starts booting from the SD and then loads the OS from an external HDD.

Follow it through and stop just when it tells you to "Install Apache2" and you'll be good to go.

 

[ZXSpectrum]

Thanks Very much Mr Feek sir!