Run Retropie from USB Hard Drive WITHOUT the need for SD card at all! You might want to back up your SD card before doing this!

My method will allow you to take one of your existing Retropie images that you use and love and transfer it to a USB drive – which will give you more space for more roms!

From the Retropie command line type the following:

sudo apt-get update && sudo apt-get install rpi-update

sudo BRANCH=next rpi-update

echo program_usb_boot_mode=1 | sudo tee -a /boot/config.txt

reboot

From a command line again:

vcgencmd otp_dump | grep 17:

** Make sure it returns 17:3020000a

Keep in mind in the next few steps you are going to modify the files that let you boot up from your SD card and it will not boot from it anymore unless you re-image it. This is to you can create a USB bootable image and save it to your hard drive in Windows while retaining all your Retropie settings and roms. You might want to back up your SD card before continuing.

From a command line in Retopie type the following:

sudo sed -i "s,/dev/mmcblk0p2,/dev/sda2," /etc/fstab

sudo sed -i "s,/dev/mmcblk0p,/dev/sda1," /etc/fstab

You are basically changing mmcblk0p1 to sda1 and mmcblk0p2 to sda2 in /etc/fstab.

sudo sed -i "s,root=/dev/mmcblk0p2,root=/dev/sda2," /boot/cmdline.txt

You are basically changing root=/dev/mmcblk0p2 to root=/dev/sda2 in /boot/cmdline.txt

Now that your OS and firmware are updated and you have toggled OTP bit on your Pi to allow it to boot from USB, shutdown Retropie and take out the MicroSD card and then copy via Win32diskimager to your Windows hard drive. Once that is done remove your MicroSD card from WIndows and plug in your USB drive into your Windows PC, and use Win32diskimager to write that image you just saved onto your USB drive. Once it's done remove the USB drive from Windows and plug it into your Pi via a USB hub into a USB port.

Once booted you will have to resize to get all the space of the new drive.

You will have to do this manually via the command line in Retropie because the built-in tools to do so in Retropie do not like the USB hard drive. It may work with a USB flash drive as I did not test this. Anyhow here is how you do it manually. Log into Retropie via ssh or by going into the program and exiting Emulation Station which will put you at the command line:

1.) sudo fdisk -l

Look at the bottom of the output and pay attention to the very last line which contains /dev/sda2. The second column of this line shows the starting sectors for this parition (for example, in my case it was 124928 – it will be different depending on your hard drive. Remember or write down this number – it is very important!

2.) fdisk /dev/sda

3.) Press d <Enter>

4.) Press 2 <Enter>

Now re-create it:

5.) Press n <Enter>

6.) Press p <Enter>

7.) Press 2 <Enter>

8.) Enter the First sector and the same value as the original /dev/sda2 partition (124928 from the above example).

9.) For the Last sector just press enter to use the maximum value.

10.) Now press 'p' > Enter to see the new partition setup.

11.) Finally press 'w' > Enter to write it

12.) type sudo reboot

13.) After reboot finishes and your are back in Retropie go back to the command line using ssh method or by shutting down Emulation Station method.

14.) sudo resize2fs /dev/sda2

This could take a little while. Let it complete. When you get your command line prompt back type in

df -h

and look at the size of /dev/root. You should see all your new space available. I started out with a 128 GB image and SAD card and now this is what it looks like since I upgraded to a 1 TB hard drive:

Filesystem Size Used Avail Use% Mounted on

/dev/root 918G 205G 685G 23% /

NOTE: My USB hard drive works with and without a USB hub but it is recommended to use a hub since the drive will draw too much current from the Pi and possible wreck it.

SOURCE : Tom Gellert