I recently switched to Ubuntu 22.04 on my Raspberry Pi 4 and faced an issue with trying to use the full space on my RAID cabinet (Icy Box IB-RD3640SU3E2). The parition table type MBR is no good for such cases and that is what one gets after writing the installer on the USB drive with rpi-imager. What to do?
Fortunately there is a convenient tool called mbr2gpt (don’t bother with gparted, it failed me at least) which does the conversion in-place without data loss (at least the two times I have used it…).
The process for a fresh Ubuntu 22.04 installation on an external USB connected drive (for example a RAID cabinet as outlined above).
1. Use rpi-imager to write Ubuntu 22.04 preinstalled image to the usb drive and to a SD card
2. Boot with the USB drive plugged in and go through the Ubuntu installation guide
3. Boot with the SD card plugged in and without USB drive and go through the Ubuntu installation guide.
4. Boot with the SD card but without USB drive, then plug in the USB drive when Ubuntu has started. Unmount the USB drive if it is mounted.
5. Use the mbr2gpt utility to convert mbr to gpt and expand the root partition (sudo mbr2gpt /dev/sda). Choose to expand the root filesystem and not to boot from SD card.
6. Reboot without the SD card.
If you have to also restore a previous backup (for example a simple tar archive done with tar cvf /backup.tar --exclude=/backup.tar --exclude=/dev --exclude=/mnt --exclude=/proc --exclude=/sys --exclude=/tmp --exclude=/media --exclude=/lost+found \ /), like in my case, this would be the additional steps:
7. Start with the SD card and without USB drive.
8. Mount the USB filesystem on /media/new and create /media/backup
9. Mount the filesystem with backup file: mount -t nfs serve:/media/backupdir /media/backup
10. Make a backup of /media/new/etc/fstab and /media/new/boot/firmware/cmdline.txt
11. Copy the backup to USB drive’s filesystem: tar xvf /media/backupdir/backup-file.tar -C /media/new
12. If you refer to PARTUUIDs in fstab or cmdline.txt, restore to match the partition UUID from the backup
13. Reboot without the SD card and hopefully the system boots fine (like it did for me…)