Hardware hookup here is pretty simple:
- Plug USB hub into a free USB port on the Pi.
- Plug power cable into powered USB hub.
- Plug external drive into USB hub.
In the case where you're using a USB thumb drive, you can likely just plug right into the Pi.
Power on the Pi, if you haven't already, and bring up a terminal. Next, let's see if the drive showed up. First, try lsusb:
The line Bus 001 Device 005: ID 0bc2:ab24 Seagate RSS LLC looks promising. You'll likely see something similar, although the device isn't guaranteed to have a manufacturer string.
So next let's figure out where the drive actually shows up on the filesystem. Try using dmesg:
Here're the lines of interest:
[ 8.822011] sd 0:0:0:0: [sda] Write cache: enabled, read cache: enabled, doesn't support DPO or FUA [ 8.849001] sda: sda1 [ 8.862459] sd 0:0:0:0: [sda] Attached SCSI disk
Your output will probably look a little different, but unless you have another USB drive plugged in, your drive is almost certain to be /dev/sda.
Once you know what drive to target, you can use a helper script we've written called adafruit-pi-externalroot-helper. The source for this script can be found here on GitHub.
If you're already using our package repository, you can install the script and run it like so:
sudo apt-get install adafruit-pi-externalroot-helper sudo adafruit-pi-externalroot-helper -d /dev/sda
Want to use our packages? Check out this guide to using the Adafruit Raspberry Pi package repository.
If you're using a stock Raspbian install, and would rather not mess around with the package manager, try this instead:
git clone https://github.com/adafruit/Adafruit-Pi-ExternalRoot-Helper.git cd Adafruit-Pi-ExternalRoot-Helper ./adafruit-pi-externalroot-helper -d /dev/sda
You'll be prompted to continue - double-check that the script is pointed at the right drive, and press y to continue.
This will take a long time.
It first creates a new filesystem on the target drive and copies everything on your root filesystem there using rsync. Lastly, it alters the kernel boot parameters in /boot/cmdline.txt and modifies a file called /etc/fstab to stop mounting the old root partition on the SD card.
Once the script is finished, you might want to check the contents of the following files:
/mnt/etc/fstab: the old /dev/mmcblk0p2 entry for root should be commented out, and there should be a new one for your external device, identified by a path including a long unique id. Mine looks like this:
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, so no using swapon|off from here on, use dphys-swapfile swap[on|off] for that /dev/disk/by-uuid/8bc7fb29-43c4-4179-9a32-89df37badad3 / ext4 defaults,noatime 0 1
/boot/cmdline.txt: Instead of root=/dev/mmcblk0p2, you should see a root=PARTUUID=... parameter. Mine looks like so:
dwc_otg.lpm_enable=0 console=ttyAMA0,115200 console=tty1 root=PARTUUID=ED5E1D73-8EAA-4C40-99A6-1E3A3795F98C rootdelay=5 rootfstype=ext4 elevator=deadline rootwait fbcon=map:10 fbcon=font:VGA8x8
When you reboot, /mnt/etc/fstab will be the new /etc/fstab. (The Arch Linux wiki has a pretty good explanation of what this file does.)
If everything looks in order here, go ahead and reboot like so:
sudo reboot
Once your Pi boots, you can log in like normal and try a couple of commands.
df -h
This should show /dev/root with its amount of drive space free, which should correspond to what's available on your new drive. This is probably a good enough indication, if you're using a drive bigger than your SD card, but you can also check that /dev/root points to /dev/sda1:
readlink /dev/root
...and you should be able to look in /dev/disk/ and see that it's available by its unique ID:
ls -l /dev/disk/by-uuid ls -l /dev/disk/by-label
...and verify that it's mounted on /:
mount | grep root
These should show that /dev/sda1 is
If for some reason your Pi doesn't boot, you can restore things by opening the first partition on the SD card from another machine (Windows or OS X will work just fine) and editing cmdline.txt.
Just replace root=PARTUUID=... rootdelay=5 with root=/dev/mmcblk0p2, which will point the root partition back to the second partition on your SD card, looking something like this:
dwc_otg.lpm_enable=0 console=ttyAMA0,115200 console=tty1 root=/dev/mmcblk0p2 rootfstype=ext4 elevator=deadline rootwait fbcon=map:10 fbcon=font:VGA8x8
Put the card back into the Pi, and it should boot like normal.
Page last edited April 09, 2015
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