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.


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 /

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:

├─sda1      system-boot 20945b24-01
└─sda2      writable    20945b24-02
├─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.


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 JPJ

    Hi James A., I had to change the fstab entry for rootfs before rebooting (see “updating fstab”). Otherwise the pi wasn’t starting.

    Cheers James P.

  2. Avatar for Søren Frank

    I just got my Pi 4 4GB, and after setting up USB boot, it completely bricked itself. I tried new images, SD cards and even flashing the new built in EEPROM, but nothing works. Both LED’s are on. Are there any steps to revert the change?? Or is it completely dead…

    1. Avatar for jamesachambers

      Hey Søren,

      The changes in this guide only live on your SD card / main partition. Flashing the new built in EEPROM would have been my suggestion but honestly it sounds like this may be a defective board.

      All that is needed to revert all the changes in this guide is to reformat the SD card basically. Unlike the Pi 3 there is no program_usb_boot_mode=1 that permanently flip a bit in your Pi or anything like that.

      Have you tried a different power cable? One of the commenters in my other article figured out that his power supply was to blame for a similar issue.

  3. Avatar for Steve

    Hello all,
    Thanks very much for the guide. The part that caused me grief was the alteration to /boot/cmdline.txt. In a nutshell, I found cmdline.txt can only have ONE line of text in it or it ignores any alteration. Unless I erased the original content entirely and copied a simliar line to the original with the changed PARTUUID it refused to work.
    Commenting out the original text and copying to a line below would not work at all, it had to be removed, with cmdline.txt consisting of just one line of ‘new’ text before it would boot from the ssd. Hope that helps.

      1. Avatar for Steve

        I think I should have made it clear I’m using a pi4/4Gb and only using the root (ie /) partition on the ssd until they incorporate pxe and usb boot. boot partition of course remains on the sdcard for now. As you know, both can be on the ssd when using a pi3. Thanks again for the guide, I wouldn’t be this far if it wasn’t for that!

  4. Avatar for kobun

    Thank you for the useful article.
    It is the result of my Pi4 + JMicron + Samsung 830 120G SSD.(USB3 hub is not used)

    #lsusb | grep JMicron
    Bus 002 Device 002: ID 152d:0567 JMicron Technology Corp. / JMicron USA Technology Corp. JMS567 SATA 6Gb/s bridge

    #dd if=/dev/zero of=/var/test bs=8k count=500k conv=fsync
    512000+0 records in
    512000+0 records out
    4194304000 bytes (4.2 GB, 3.9 GiB) copied, 23.1891 s, 181 MB/s

  5. Avatar for AndyOfLinux

    Maybe it’s obvious BUT after getting the external SSD drive working, you should do a “raspi-config” and “apt-get” update, upgrade, and dist-upgrade. This is to get the USB drive updated with the latest — as the first time run as mentioned in the post was for the SD Card 😉 If you see a “testing” vs “release” error message with “sudo apt-get update”, try “sudo apt update” and say “y” to updating repository.

    1. Avatar for Jeffeb3

      Yeah, there is an update step when running from the sdcard, but that won’t apply to the root partition on the USB drive.

  6. Avatar for Alex

    The Orico 2139U3 (R1.0) works well for me with Pi 4 and Intel 520 series 120GB SATA SSD. Boot on SD card, root on SSD.

    1. Avatar for AndyOfLinux

      Bad news for me. I bought 2 of this enclosure (Orico 2139U3) from Amazon (per the link) and it does NOT work with my Crucial BX500 SSD 🙁 “lsusb” shows a JMicron controller.

  7. Avatar for Patrick

    I plan to set up a Minecraft Server for me and my friends on a Rasp 4 with 4gb Ram, and I wonder if a external power supply for the SSD would make a difference.
    I’m talking about products like this one

    What are your thoughts on this?

    1. Avatar for jamesachambers

      With past Pis it generally has been okay to power it using the Pi’s onboard USB ports
      However on the Pi 4 (even though it has more power) it could definitely be more stable to power the hard drive externally like with this adapter.
      The only question then will be compatibility. If you try it and it works let us know!

      1. Avatar for dzm

        tl;dr: It can’t hurt to have external power for any USB devices, but I’ve had better luck with the Pi4 power and no external USB power.

        Longer: I’ve had absolutely no problem powering two SSD drives from the Pi4 using the Pi-branded USBC power supply. With a Pi3 using the same SATA/USB adapter I’m using with the Pi4 I would get low-power resets when powering the system from a 2A USB-A power supply.

    1. Avatar for jamesachambers

      Hey sozen,

      The Raspberry Pi 4 does not have this boot mode support like the 3 series yet featured in the link. The Raspberry Pi foundation is working on adding this back in but for the moment you need to do a workaround like my article to get a USB rootfs.

  8. Avatar for dzm

    This adapter appears to be working (Updated: read reply): https://www.amazon.com/gp/product/B07FDTY299

    It might be worth nothing that on first reboot onto the SSD there will be a loooong period of LED blinking with not viable network. This seems to be normal and not a “oh no, things aren’t working” situation. It might also be worth mentioning that this whole thing is needed due to the “boot from USB” instructions for Pi3 no longer working, AND that creating the “ssh” file onto /boot of the SSD drive will be necessary even if you’ve already been using SSH into a headless Pi4 booting from the memory card.

    Thanks for the instructions! While this has still been a pain, you’ve saved me lots of time.

    1. Avatar for dzm

      Update: The adapter I mention above seems to suffer from really bad I/O performance. Avoid it, at least for now (I haven’t determined if it ALSO has bad I/O performance when it’s just a USB device hanging off a Pi4 running from the card). This one [ StarTech 2.5″ SATA to USB Adapter ] appears to be working though.

      # lsusb | grep SATA
      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

      # dd if=/dev/zero of=/root/test bs=8k count=500k conv=fsync
      512000+0 records in
      512000+0 records out
      4194304000 bytes (4.2 GB, 3.9 GiB) copied, 18 s, 233 MB/s

      Looks like it’s the same chipset/device that Krikkit is reporting success with, though packaged up by a different vendor. I seem to be getting even better I/O than Krikkit is, too. Neat!

    2. Avatar for dzm

      Further update: The adapter mentioned in my original response is evidently a JMicron chipset:

      # lsusb | grep JMicron
      Bus 002 Device 003: ID 152d:0578 JMicron Technology Corp. / JMicron USA Technology Corp. JMS567 SATA 6Gb/s bridge

      I’ve confirmed that the I/O for this adapter is just abysmal on the PI4 USB3 bus. Haven’t tried it on the USB2 bus yet.

      1. Avatar for dzm

        More followup:
        Using the JMicron adapter (above, with the extremely bad I/O performance when plugged into the USB3 ports) can produce reasonable results if you plug it into an intermediary USB3 hub. I’ve plugged it into this one [ https://www.amazon.com/gp/product/B00DQFGH80 ]and am now seeing:

        # sudo dd if=/dev/zero of=/mnt/sdb_btrfs/test bs=8k count=500k conv=fsync
        512000+0 records in
        512000+0 records out
        4194304000 bytes (4.2 GB, 3.9 GiB) copied, 21.6255 s, 194 MB/s

        For comparison here’s another drive (the /root drive, a PNY 120GB SSD) using the ASM1051E chipset (the “StarTech” mentioned above) connected directly to the USB3 bus (NOT going through an intermediary hub):

        # sudo dd if=/dev/zero of=/mnt/test bs=8k count=500k conv=fsync
        512000+0 records in
        512000+0 records out
        4194304000 bytes (4.2 GB, 3.9 GiB) copied, 16.5049 s, 254 MB/s

        The difference in performance could be due to the USB hub not being great, or the JMicron already known to be janky, or the 60GB SSD in it not being new and fancy like the PNY. Hard to say. Still, the 194MB/s is certainly better than the ~30MB/s it was hitting on the USB2 interface, and WAY better than the I/O Timeout errors it was sporadically throwing from the USB3 interface.

    3. Avatar for jamesachambers

      Hey dzm,

      Thanks for the feedback, I’m glad it was able to help save time! I’ve added your suggestions in the article in new/updated sections to hopefully save others even more time going forward!

    4. Avatar for dzm

      Additional learnings after a bit of goofing around:

      * The JMicron adapter still works as expected on the USB2 bus. It’s just really sad. ~30MB/s vs ~231MB/s for the ASMedia adapter on the USB3 bus.
      * The USB3 + SSD combination has MUCH better I/O performance than my SanDisk micro-SD card.
      * Seems as though there’s no good way to get btrfs running on the partition that holds the kernel and modules. I’ll need to do decide if I care enough about getting the whole (mostly) system onto btrfs, or am OK with the OS parts of the filesystem on the default ext4 and just remap the data I care about (databases, /etc, etc) remapped into paths in a btrfs hierarchy
      * Haven’t yet done a power comparison versus the Pi3 for my work loads. The Pi3 was pulling ~4 watts for my workload and was much, much slower. I’m curious to see if the Pi4 with the same workload (though updated to Buster, with 2GB RAM, quad-core and faster CPU) stays within the same budget of <10 watts.
      * Migrating from the Pi3 to the Pi4 has reminded me, again, what a pain it is to backup/restore Linux in general. Dependency hell, configurations and data scattered across many many directories, incompatible configuration changes from one version of a distro to another, etc. Keep good notes! You'll need them again in the future. 🙂

      All-in-all the Pi4 is an amazing upgrade from the Pi3. You never really think of how constraining the Pi3 is until you get a to do the same work on a more robust system (as opposed to doing a lot of work on an EC2 instance where you expect the performance to be different and thus don't really compare it to the micro-work you're doing on the Pi). Just looking forward to the improvements in USB3 support as they move forward (native USB and/or network booting would be fantastic).

  9. Avatar for krikkit

    Sabrent USB 3.0 to 2.5″ SATA adapter does not work with my raspi 4 4 gb, sorry i have 2 of them 🙁

    …just tried my other adapter:
    CSL SL – USB 3.0 auf SATA Adapter

    root@raspi4:~# lsusb
    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

    AND it is WORKING!!! …quick test with dd showed the following stats:

    root@raspi4:~# sudo dd if=/dev/zero of=/root/test bs=8k count=500k conv=fsync
    512000+0 records in
    512000+0 records out
    4194304000 bytes (4.2 GB, 3.9 GiB) copied, 25.3591 s, 165 MB/s

    1. Avatar for jamesachambers

      Those are beautiful numbers! Thanks for letting us know, I’ll add it to the list of working adapters!

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