Raspberry Pi 4 USB Boot Config Guide for SSD / Flash Drives

Raspberry Pi 4 with Samsung 950 Pro NVME SSD
Raspberry Pi 4 with Samsung 950 Pro NVME SSD

The Raspberry Pi 4 is finally here and has a lot of exciting changes. One very major downside is that it doesn’t support true USB booting yet out of the box (like the 3 series did). The Raspberry Pi foundation states that it is being worked on and will be added back with a future update. No timeline has been given yet for that to happen but they state it’s one of their top priorities.

Most of my projects heavily depend on having good performing storage so sitting and waiting was not an acceptable solution. In this guide I’ll show you a workaround to use USB devices as your rootfs device and use a Micro SD card as bootloader only which gives us full SSD performance after boot! To see exactly how much of a performance difference this makes (spoiler: it’s gigantic) check out the Raspberry Pi Storage Benchmarks.

I highly recommend doing this on a completely new install. If you try to upgrade your old ones and something goes wrong there’s a good chance you might lose data. We will be modifying the boot partition, resizing partitions, etc. so don’t use a drive with any data on it unless you are positive you have all of the steps down!

Compatible USB 3.0 Adapters

The Raspberry Pi 4 is proving to be picky about what SATA, M.2, etc. adapters will work in the USB 3.0 port. The USB 3.0 ports are the ones in the middle that are blue inside. The black ones are USB 2.0 and won’t give you the faster speeds the new Pi offers.

It’s very likely that some of these will be fixed via software and firmware updates and the Raspberry Pi Foundation has several open known issues related to USB 3. Until that happens though I will maintain a list here of known working ones and known problematic ones. It’s still very early in the release of the Pi 4 so we still have a lot to learn about which adapters work / don’t work. If you have working and nonworking adapters leave a comment and I’ll add it in this list.

If the adapters worked before on older Pis then one thing you can try is putting them in the black USB 2.0 ports. Obviously this is stupid because we all want the Pi 4 performance gains but if you end up needing to buy a new adapter this will give you a workaround until a replacement arrives!

Find USB adapter chipset

There are certain chipsets used in adapters that are known to be working/not working.

pi@raspberrypi:~ $ lsusb
Bus 003 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub
Bus 002 Device 002: ID 174c:55aa ASMedia Technology Inc. Name: ASM1051E SATA 6Gb/s bridge, ASM1053E SATA 6Gb/s bridge, ASM1153 SATA 3Gb/s bridge, ASM1153E SATA 6Gb/s bridge
Bus 002 Device 001: ID 1d6b:0003 Linux Foundation 3.0 root hub
Bus 001 Device 002: ID 2109:3431 VIA Labs, Inc. Hub
Bus 001 Device 001: ID 1d6b:0002 Linux Foundation 2.0 root hub

This is a lsusb dump of all my connected USB devices. I have bolded the line with the USB bridge device. We can see that the chipset is ASM1153E

Known Good Chipsets

  • ASMedia ASM115X (StarTech 2.5″ SATA)

Known Working Adapters

2.5″ SATA

StarTech.com 2.5″ SATA to USB Cable

Confirmed working by dzm in the comments

ELUTENG 2.5″ SATA to USB 3.0

The ELUTENG is one of the known working 2.5″ SATA to USB 3.0 adapters for the Pi 4.

CSL SL – USB 3.0 auf SATA Adapter

The CSL SL adapter is confirmed to be working by Krikitt in the comments. Might not be available in the US.

M.2 Adapters

Shinestar M.2 NVME to USB Adapter

This is the adapter I’m using in the picture at the top of the article. It is for NVME M.2 drives.

QNINE M.2 SATA to USB Adapter

I used this adapter to benchmark M.2 SATA Lite-On and SanDisk drives — working great in 3.0 ports.

mSATA

Tanbin mSATA Micro SATA to USB Adapter

I used this mSATA to USB adapter for my Crucial M550 benchmark — working in 3.0 ports.

fe2008 mSATA to USB 3.0 Adapter

Confirmed working in comments by Nico

Power Adapters

Canakit USB-C Raspberry Pi 4 Power Supply

Known Problematic Adapters

USB Boot Instructions

  1. Prepare Bootloader SD Card – Image your SD card with the latest Raspbian 10 “Buster” release (I prefer Raspbian Lite) however you would normally do it.
  2. Prepare SSD / Flash Drive – Image your SSD or Flash Drive. Make sure you create the empty file named “ssh” on the boot partition of both drives.
  3. Boot / Update Raspberry Pi – Start up your Raspberry Pi with only the SD card in the slot. After the Pi finishes booting up plug in your SSD / Flash drive.
  4. Run sudo blkid – With your SSD / Flash drive plugged in type the command “sudo blkid” (example below)
  5. Identify drive – Your list will contain /dev/mmcblk0p1 and 2 (SD card) and your SSD / Flash drive (usually/dev/sda1 and 2).
    We are looking for the PARTUUID of your flash / SSD drive’s second partition (rootfs). This will end with -02. Here is an example:
    /dev/sda2: LABEL=”rootfs” UUID=”638417fb-7220-47b1-883c-e6fee02f51ac” TYPE=”ext4″ PARTUUID=”0634f60c-02″
    Save or white a note somewhere of the values for both drives. We will use both PARTUUIDs for /dev/sda* and dev/mmcblk* later.
  6. Edit /boot/cmdline.txt – First make a backup by typing: sudo cp /boot/cmdline.txt /boot/cmdline.txt.bak
    Now type “sudo nano /boot/cmdline.txt” – Change your boot command to load the partition from the SSD / Flash drive instead of your SD card.
    Before: dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=PARTUUID=af1800e7-01 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait
    After: dwc_otg.lpm_enable=0 console=serial0,115200 console=tty1 root=PARTUUID=0634f60c-02 rootfstype=ext4 elevator=deadline fsck.repair=yes rootwait
  7. Reboot Pi – If your Pi won’t boot put your micro SD into a computer and restore /boot/cmdline.txt.bak to get back into the Pi.
    Note: the first boot with your SSD / Flash drive will be slow the first time as it runs fsck on the drive and other first boot configuration.
    It can take over a minute or two sometimes for really big drives so give it a little bit of time here before assuming it didn’t work
  8. Update fstab – Change /etc/fstab entry for /boot to point to the SD card to ensure that firmware and bootloader updates retrieved — detailed example/instructions in section below. Reboot after updating fstab.
  9. Resize file system – Upon first startup the size of your root (/) filesystem partition will only be 1.8G no matter how big your drive is — see section below for detailed example/instructions
  10. Update Pi – Type “sudo apt-get update && sudo apt-get dist-upgrade” to update the system and firmware.

Your system will now be running completely from your USB drive! To verify this, run the command “findmnt -n -o SOURCE” / to ensure your root partition has switched over as shown below to /dev/sda2 instead of /dev/mmcblk0p2.

pi@raspberrypi:~ $ findmnt -n -o SOURCE /
/dev/sda2

Updating fstab

Right now your fstab file on the USB drive is automounting the /boot/ partition from the USB drive even though it isn’t being used. We need to update this to your SD card so that firmware/bootloader updates are actually utilized.

Get Device PARTUUIDs

First lets get a list of all storage devices attached to the Pi and their IDs (we will use these later). Type the following command:

lsblk -o name,label,partuuid

This will output a device tree with the name and label of each partition and the PARTUUID. The tree looks like this:

NAME        LABEL       PARTUUID
sda
├─sda1      system-boot 20945b24-01
└─sda2      writable    20945b24-02
mmcblk0
├─mmcblk0p1 system-boot f65c7036-01
└─mmcblk0p2 writable    f65c7036-02

We see that we have two storage devices attached (sda and mmcblk0). Each of these devices also has two partitions. Notice that both devices have a partition with the label “system-boot”. This is our target.

Edit /etc/fstab File

We are now ready to edit the /etc/fstab file. To begin editing the file type:

sudo nano /etc/fstab

Your current file will look like this:

cat /etc/fstab
proc                  /proc           proc    defaults          0       0
PARTUUID=20945b24-01  /boot           vfat    defaults          0       2
PARTUUID=20945b24-02  /               ext4    defaults,noatime  0       1

We want to change the /boot partition (ending with -01) to load our Micro SD cards PARTUUID instead of the USB drives. To do this simply replace the PARTUUID field on the line that has /boot in it with the PARTUUID from mmcblk0p1. After making the change my /etc/fstab file looks like this:

proc                  /proc           proc    defaults          0       0
PARTUUID=f65c7036-01  /boot           vfat    defaults          0       2
PARTUUID=20945b24-02  /               ext4    defaults,noatime  0       1

Press Ctrl+X to tell nano to save our changes.

Now type sudo reboot to restart the Pi.

Enable SSH on Micro SD Partition

Make sure the SD card and new drive both have a blank “ssh” file if you want to keep SSH enabled. Even if you had it on your USB storage device if you didn’t create one on your SD card the next time you reboot you won’t be able to SSH in.

ot. After reboot typing: “df -H” should show /boot/ as being the SD card again (mmcblk0). Now we can be sure that any updates to the /boot/ partition from apt-get are applying to our system.

Resizing Filesystem

By default the partition on the SSD / Flash drive will only be 1.8G. The Pi expands this automatically on micro SD drives but we will need to do it ourselves for a SSD / Flash drive. To do this we need to expand the partition and then resize the file system.

First let’s open fdisk and print the partitions:

pi@raspberrypi:~ $ sudo fdisk /dev/sda

Welcome to fdisk (util-linux 2.33.1).
Changes will remain in memory only, until you decide to write them.
Be careful before using the write command.
Command (m for help): p

Disk /dev/sda: 238.5 GiB, 256060514304 bytes, 500118192 sectors
Disk model: 2115
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 33553920 bytes
Disklabel type: dos
Disk identifier: 0x0634f60c
Device     Boot  Start     End Sectors  Size Id Type
/dev/sda1         8192  532480  524289  256M  c W95 FAT32 (LBA)
/dev/sda2       540672 4292607 3751936  1.8G 83 Linux

There is the line we need. Our start value for /dev/sda2 (rootfs) is 540672. Next we need to remove and recreate the partition as a larger size. If you make any mistakes during this command just close fdisk by pressing q. The changes won’t be written to disk. If you mess up any of the commands the drive will no longer boot and you’ll have to start over again so be careful!

Command (m for help): d
Partition number (1,2, default 2): 2
Partition 2 has been deleted.
Command (m for help): n
Partition type
    p   primary (1 primary, 0 extended, 3 free)
    e   extended (container for logical partitions)
Select (default p): p
Partition number (2-4, default 2): 2
First sector (532481-500118191, default 589815): 540672 (enter the start value exactly as it was, the default will be wrong)
Last sector, +/-sectors or +/-size{K,M,G,T,P} (540672-500118191, default 500118191): (press enter to accept default which is the full disk)
Created a new partition 2 of type 'Linux' and of size 238.2 GiB.
Partition #2 contains a ext4 signature.
Do you want to remove the signature? [Y]es/[N]o: n (don't remove signature)

If everything went well then type “w” and press enter. Otherwise press “q” to quit and try again. Once you enter “w” the changes will be permanently written to disk!

Now reboot the system. Type “df -h” to view the current disk:

pi@raspberrypi:~ $ df -h
Filesystem      Size  Used Avail Use% Mounted on
/dev/root       1.8G  1.2G  450M  73% /
devtmpfs        866M     0  866M   0% /dev
tmpfs           995M     0  995M   0% /dev/shm
tmpfs           995M  8.4M  987M   1% /run
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           995M     0  995M   0% /sys/fs/cgroup
/dev/sda1       253M   40M  213M  16% /boot
tmpfs           199M     0  199M   0% /run/user/1000

We can see our disk is still 1.8G even after resizing the partition. That’s because we still have one more step! We need to resize the filesystem to fill our new partition space. For this we will use “sudo resize2fs /dev/sda2”:

sudo resize2fs /dev/sda2
resize2fs 1.44.5 (15-Dec-2018)
Filesystem at /dev/sda2 is mounted on /; on-line resizing required
old_desc_blocks = 1, new_desc_blocks = 15
The filesystem on /dev/sda2 is now 62447190 (4k) blocks long.

Now let’s check df -h again:

Filesystem      Size  Used Avail Use% Mounted on
/dev/root       235G  1.2G  224G   1% /
devtmpfs        866M     0  866M   0% /dev
tmpfs           995M     0  995M   0% /dev/shm
tmpfs           995M  8.4M  987M   1% /run
tmpfs           5.0M  4.0K  5.0M   1% /run/lock
tmpfs           995M     0  995M   0% /sys/fs/cgroup
/dev/sda1       253M   40M  213M  16% /boot
tmpfs           199M     0  199M   0% /run/user/1000

And that’s it! You will now be using all of your space on your SSD / Flash drive.

Conclusion

The Samsung 950 Pro NVME drive in the featured picture scored a 9189 on the Raspberry Pi Storage Benchmark. The previous all-time record score on a Pi 3B+ was 3561. The performance gains are very real and very dramatic.

For me getting this performance is well worth having to waste a micro SD card just to be a bootloader. I am largely after the USB 3.0 bus and gigabit ethernet performance improvements and using this method I am able to achieve the performance I was after without waiting an indeterminate amount of time for the feature to be added back in!

Although there are ongoing compatibility issues and we lack the super easy native USB booting support we had before I’m more than willing to go through the growing pains to finally get rid that ancient USB 2.0 bus! Just make sure if you are planning to build a system you plan your adapters and parts accordingly.

179 thoughts on “Raspberry Pi 4 USB Boot Config Guide for SSD / Flash Drives”

    1. Avatar for jamesachambers

      Hey ninosr,

      Yes. For Ubuntu you will write the image to both a SD card and a SSD. Then you go into /boot/firmware/cmdline.txt and change root=/dev/mmcblk0p2 to root=/dev/sda2 and then reboot. It will then boot the root partition from the SSD (it should reset the password back to ubuntu/ubuntu).

  1. Avatar for Simon

    My fstab file does not have partuuids in it. I’ve managed to run a script to change the partuuids so there different but now im stuck.

  2. Avatar for Tman

    When booting from SD card, I can mount my USB3-connected SSD just fine. But when I follow this guide, change cmdline.txt and reboot, the pi does not start (I let it sit for 5 minutes). Is my SSD model problematic, or does it mean if I can mount it, it should work and I made a mistake somewhere?

    Also, I am a bit confused about the guide. In step 6, the before should be af1800e7-01 and not af1800e7-02? After all, I am not changing from sdcard-boot to ssd-root but from sdcard-root to ssd-root.

    And why do I would reboot the pi in step 7 before adjusting /etc/fstab so that my entry for / has the updated PARTUUID?

    1. Avatar for Tman

      But it does work now. I connected through a serial console and saw that hint about the root account being locked. So I set fsck.repair=no in cmdline.txt and then it worked.

  3. Avatar for Hendy

    i have a question, does the raspbian version in the SD card have to match the raspbian version in the SSD?
    e.g. i have a raspbian lite on the SD card, while my ssd has the minimal desktop version.

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