Running ROMs from a USB drive
Rather than running everything from an SD card, it can be desirable to store and run ROMs from an external USB drive. The benefits of this are as follows:
- Reliability: USB storage can be less sensitive to corruption than SD cards.
- Separation of data: In the event that a RetroPie installation becomes corrupted or a new image is required, any ROMs, saves, etc, are not lost. Simply remove the USB stick, re-image the SD card, re-apply these setup instructions, and all that data is retained.
- Easy ROM transfer: When the system is off, you can remove the stick and plug it into any other computer and easily copy-and-paste ROMs into the correct folders.
- Speed: USB transfer speeds can be faster than SD card transfer speeds (see http://www.roylongbottom.org.uk/Raspberry%20Pi%20Benchmarks.htm#anchor21).
- Cost: USB storage tends to be cheaper than the equivalent microSD card.
- Capacity: USB storage can reach huge capacities, whereas microSD is limited.
- Compatibility: microSD cards suffer from compatibility issues with Raspberry Pi systems. USB storage devices should mostly all work.
There are a number of ways you can achieve this, but the following method is desirable as it fully integrates the USB drive with the existing directory structure, rather than requiring you to tweak configuration files so RetroPie is looking for ROMs in a different place. Below there are two ways to accomplish this: an automated method, or a manual method.
Format USB drive
Either on linux, or on a PC, format the USB drive to FAT32 (used in this guide as it is the most compatible across different operating systems).
- Instructions to format on Linux
- Instructions to format on Windows (various)
- Instructions to format on OSX
Automatic Mount (Easiest Method)
As of December 30, 2016 a simple automated method was added to run roms from a USB drive.
- First Update the RetroPie Setup Script
- Re-Enable the USB ROM Transfer Service
- Format your USB drive to FAT32 per directions above
- Create a folder called
retropie-mounton the USB drive
- Plug into Raspberry Pi
- It will proceed to automatically copy the
RetroPiefolder AND all of its contents (you may need to reboot to start the copying)
NOTE if you have a large ROM collection already on the SD card it will copy all of the ROMs too so make sure your USB is large enough. It is easiest if you haven't added any roms yet.
Once the folder structure is copied over the USB will be mounted over the RetroPie folder so any ROMs you add to your pi will be run off of the USB.
After formatting your USB based on the above step:
Disable USB transfer daemon
- Enter the RetroPie Setup menu within the RetroPie menu in EmulationStation.
- Select Setup / Tools.
- Select usbromservice - USB ROM Service
- Disable USB ROM Service.
Plug in USB drive
This can be done when the system is powered on.
Transfer the existing RetroPie file structure
This step is mandatory regardless of whether you have any roms on your system. RetroPie has a specific directory structure and a number of files required packaged with even empty installations.
Either via SFTP, or using the terminal (via exiting emulationstation, pressing F4, or remotely using [[SSH]]), move the
/home/pi/RetroPie folder into your USB stick. The reason for moving the whole folder, and not just
/home/pi/RetroPie/roms is that there are other folders, such as /home/pi/RetroPie/BIOS` that are worth keeping on the external drive also.
To do this via terminal, First enter the command
df to print a list of the file systems. Example output:
pi@retropie:~ $ df Filesystem 1K-blocks Used Available Use% Mounted on /dev/root 7318456 3367852 3609928 49% / devtmpfs 372100 0 372100 0% /dev tmpfs 376436 0 376436 0% /dev/shm tmpfs 376436 5424 371012 2% /run tmpfs 5120 4 5116 1% /run/lock tmpfs 376436 0 376436 0% /sys/fs/cgroup /dev/mmcblk0p1 58234 20476 37758 36% /boot /dev/sda1 30480256 26921632 3558624 89% /media/usb0
Look for an entry on /media/usb0, or similar. In our above example:
/dev/sda1 30480256 26921632 3558624 89% /media/usb0
The important things to note down are the mount point:
/media/usb0, and the position on the device tree:
Now we can move our existing RetroPie folder to our new USB drive. Enter the command:
sudo mv -v /home/pi/RetroPie/* /media/usb0/
After this, the USB directory structure should look something like:
pi@retropie:~ $ ls /media/usb0 -l total 96 drwxrwxrwx 8 root root 16384 Jun 15 00:17 BIOS drwxrwxrwx 3 root root 16384 Apr 22 17:05 retropiemenu drwxrwxrwx 52 root root 16384 Jun 3 00:11 roms drwxrwxrwx 2 root root 16384 Apr 13 16:14 splashscreens
Configure fstab to automatically mount USB drive
Establish the drive's UUID number by entering the command
ls -l /dev/disk/by-uuid/. Example output:
pi@retropie:~ $ ls -l /dev/disk/by-uuid/ total 0 lrwxrwxrwx 1 root root 15 Jun 19 21:59 7cc81461-50b9-45a8-a561-fd5c4aa71934 -> ../../mmcblk0p2 lrwxrwxrwx 1 root root 15 Jun 19 21:59 AE51-7D54 -> ../../mmcblk0p1 lrwxrwxrwx 1 root root 10 Jun 19 21:59 E44B-FC4E -> ../../sda1
sda1 was our device tree position from earlier (the section above describes how to find this), so
E44B-FC4E is our UUID.
Edit fstab with this command:
sudo nano /etc/fstab and add a new line like the below:
proc /proc proc defaults 0 0 /dev/mmcblk0p1 /boot vfat defaults 0 2 /dev/mmcblk0p2 / ext4 defaults,noatime 0 1 # a swapfile is not a swap partition, no line here # use dphys-swapfile swap[on|off] for that UUID=E44B-FC4E /home/pi/RetroPie vfat nofail,user,uid=pi,gid=pi 0 2
UUID= the UUID of your drive, and everything else is the same as the example. Note that each item is tab delimited. If you use spaces instead of tabs this will not work.
In the case of errors with ext4 file systems use
UUID="XXXXXXXX-XXXX-XXXX-XXXX-XXXXXXXXXXX" /home/pi/RetroPie ext4 nofail,defaults 0 0
In the case you want to allow execution of file with fat32 file system (E.g : OpenBOR), use
UUID=E44B-FC4E /home/pi/RetroPie vfat rw,exec,uid=pi,gid=pi,umask=022 0 2
This must be a full restart, not just emulationstation. When it boots up you should see any ROMs you previously had show up in emulationstation.
Now transfer ROMs either directly to the USB drive, or via any of the usual methods (aside from using the automatic USB copy, obviously!). Now that the USB drive is mounted directly to
home/pi/RetroPie, every time this directory is accessed, you're actually accessing the USB drive.