@Filofel, thanks for your report! Very interesting. Is your machine a Dell, running with HW RAID?
My experience so far with GRUB and this LP bug is that there are two things here: (a) Seems commit  might be missing in old Ubuntu releases (IIRC Xenial, but *maybe* Bionic). This might cause issues with some disks 2T+ ... (b) [And this is the main issue reported in this LP] Dell HW RAID *legacy BIOS* driver has a bug and fails to inform properly some data to Grub. In other words: imagine 5x1T disks composing a HW RAID of 5T. Grub asks BIOS data (through nativedisk likely) and the legacy BIOS driver from Dell returns data from disk 01 only - 1T of size. So, if GRUB itself (some module, for example) or the kernel/initrd are present in sectors *after* disk 01 size, it fails to load. For more reference on that, please check the following thread: https://lists.gnu.org/archive/html/grub-devel/2021-03/msg00380.html [According Dell, this is "expected" and UEFI is required!] So, your case seems a little bit different. Maybe wirth to clarify the exact model of your 4T disk, the version of Firmware (and of course the machine model) and maybe collect some GRUB logs. Interesting that you mentioned running with "--disk-module=ahci" make it works - I wonder why this isn't set by defualt on Ubuntu, likely there is a reason and I'm not aware. Cheers!  https://git.savannah.gnu.org/cgit/grub.git/commit/?id=d1130afa5f -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1918948 Title: Issue in Extended Disk Data retrieval (biosdisk: int 13h/service 48h) To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/grub2/+bug/1918948/+subscriptions -- ubuntu-bugs mailing list firstname.lastname@example.org https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs