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Hey everyone! In this post I’m going to share my experience of USB booting the Raspberry Pi 3 Model B from an SSD. Although it is something I did almost one year ago, I wanted to share it… sorry for the 1 year delay xD!

Probably there might be something I missed on my solution, so any feedback is really appreciated!

Before the pandemic started, a friend of mine sold me 4 Raspberry Pi 3 Model B and one Raspberry Pi 3 Model B+. I used them for an electronics + home automation project I no longer need anymore, so I decided to repurpose them to something new, a new project I started working on for which I will make another blog entry.

This time, as I was not going to use the RPIs for electronics, instead something that will require more disk usage, I wanted to try something I personally hadn’t tried before. I wanted to boot the RPIs from an SSD. Instead of spending money on new reliable, fast SD cards, I decided to use some spare SSDs I had instead. This is definitely something that was done before, but in my case there were some nuances that took me some days to realize how to fix them, and I wanted to share that experience with you.

What I used

For this experiment I used:

  • 4 RPI 3 Model B
  • 1 RPI 3 Model B+
  • 5 Power supplies with the proper voltage and amps
  • 5 Solid State Drives
  • 5 USB to Sata adapters

Booting from SSD

There are multiple blog posts, forum entries and now LLMs that explain how to boot a RPI from an SSD (I added references I used in the references section below). In summary the steps required for RPI 3 Model B to USB boot from SSD are the next:

  • Using an SD card with RaspberryPI OS installed, run a full upgrade: 
    sudo apt update -y && sudo apt full-upgrade -y
  • The following command will give two possible results depending on whether USB boot is enabled or not: 
    vcgencmd otp_dump | grep 17
17:1020000a <<<< it means USB boot is disabled
17:3020000a <<<< it means USB boot is enabled
  • In case it is disabled, the way to enable it is by adding the following lines to the /boot/firmware/config.txt. Some tutorials mention the /boot/config.txt but those are outdated. 
    program_usb_boot_mode=1
program_usb_boot_timeout=1
  • Finally, clone the content of the SD card that has RaspberryPI OS to the SSD, you can do that with dd: 
    # /dev/mmcblk0 is the SD card in my case
# /dev/sdb is the SSD connected via USB
dd if=/dev/mmcblk0 of=/dev/sdb status=progress
  • Then remove the SD card from the RPI, connect the SSD via USB and reboot.
  • Congrats! You booted your RPI from USB and an SSD. Now you can resize and stuff.

That’s the result I wished I had, but no, it didn’t work for 4 of my 5 RaspberryPIs. Let me tell you how I fixed-ish it.

The difference between RPI3 model B and RPI3 model B+

I executed the previous steps first (by coincidence on the RPI 3 Model B+). And it worked like a charm. Then for the next RPIs 3 Model B (not B+) it didn’t work, I tried all of the 4 RPIs with the same result. I made sure I added the program_usb_boot_timeout=1 setting to the /boot/firmware/config.txt file to increase the wait for RPI to detect the disk, even with that verification it didn’t work. No USB boot for the RPIs 3 Model B.

At that point, I got to the conclusion that at least in terms of booting, the RPI 3 Model B and RPI 3 Model B+ have differences.

My Solution (a fluke)

After trying multiple combinations that didn’t work, it booted! I checked in the terminal and indeed, it booted from SSD. I executed some IO speed tests to make sure it was indeed using the SSD. It finally worked!

The new problem was I didn’t add any new configuration change xD, so I was very confused on why it worked. And I noticed that this time I forgot to remove the SD card. Both SD and USB SSD were connected.

My hypothesis was that for RPI 3 Model B, an SD card is still required to boot, no matter if the operating system is installed on a USB SSD.

To finally verify that hypothesis, I formatted the SD card and just copied the content of the /boot/ directory from the SSD, actually they must be the same.

Voila! It booted again!

With that test, I was sure that the RPI 3 Model B requires an SD card to boot no matter where the OS is located.

I used the SD cards from my old project, formatted them and copied the content of /boot/firmware from each SSD and it worked fine.

It is important not to copy the content of the /boot/firmware directory from one SSD to all the SD cards, as each SSD has a different UUID specified in the /boot/firmware/cmdline.txt file. Copy from each SSD or make sure the /boot/firmware/cmdline.txt has the proper values for the disk UUID.

One example of the cmdline.txt

console=serial0,115200 console=tty1 root=PARTUUID=e000a75d-02 rootfstype=ext4 fsck.repair=yes rootwait cfg80211.ieee80211_regdom=US cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory

Upgrading the operating system

All the steps that I mentioned before happened when the latest RaspberryPI OS was based on Debian 12. Now the latest version of the RaspberryPI OS was released based on Debian 13, I decided that instead of formatting and doing the same process from scratch, I will follow the steps to do a RaspberryPI OS major upgrade.

These are the steps I follow for this matter:

  • Edit /etc/apt/sources.list and /etc/apt/sources.list.d/raspi.list and change from bookworm to trixie.
  • Run apt update to refresh the package indexes
  • Run apt install -y apt dpkg to install the latest version of the package manager.
  • Run apt upgrade --without-new-pkgs to install latest version without installing new dependencies. Make sure everything is fine.
  • Finally apt full-upgrade
  • Reboot

That would be enough on any setup (it works on the RPI 3 Model B+), but in this case as we boot from the SD card first and not the SSD, we will need to follow some extra steps.

Let’s recall some Linux theory: The Linux kernel image is located at the /boot directory, but in our case the RPI boots from SD. We still have the boot content from the previous installation. After the upgrade when I rebooted, the kernel was still 6.1 and not 6.12 which is the one that comes with Debian 13.

In order to have the upgrade 100% ready, I had to repeat the previous steps I did to make the RPI boot from SSD.

  • Mount the SD card mount /dev/mmcblk0p1 /mnt/sdboot/,
  • Copy /boot/firmware from SSD to the SD card: cp -r /boot/firmware/* /mnt/sdboot/
  • Reboot

After I followed those steps, I was able to have the upgrade 100% functional.

If you want to use containers

In case you want to use containers or a container orchestrator such as K3S, make sure that the fields cgroup_enable=cpuset cgroup_memory=1 cgroup_enable=memory are set in the /boot/firmware/cmdline.txt

References