GRUB2 not able to read ext4/xfs file systems on 8 TB drive

[Niklas Hambüchen]

Hello,

I'm writing to report that my GRUB2 (2.02 and 2.04) seems to have issues to 
correctly read the single ext4 and XFS file systems with ~8 TB of size on an 8 
TB hard drive.

It incorrectly shows some empty directories.

Details:

* Server: HP DL120 G7, 32 GB RAM hosted by Leaseweb
* Hard drives: 2x TOSHIBA MG05ACA8, firmware GX2A
* Partitioning scheme:
  * GPT partitions -> mdadm RAID1 -> LVM -> ext4
  * 1 MB BIOS boot partitions (sda1,sdb1), the RAID1 is over (sda2,sdb2)
  * mdadm metadata 1.2 (the current default)

Full script that shows how I'm partitioning the server:

    
https://gist.github.com/nh2/1d2c533085b514dc1a7719f6ff35640b/5592b11209777ee57ff1d96fb1341af10c2eddce

Observed the problem via 2 installation methods: This script, and the dedicated 
hoster Leaseweb's automatic reinstallation procedure of Ubuntu 18.04.
The former sets up a `(lvm/vg0-root0)`, and the latter `(md/root)`.

The problem manifests in `ls /boot` being empty even though I had checked it 
being not empty when mounted before rebooting from the installer:

    grub rescue> ls /
    ./ ../ lost+found/ opt/ dev/ bin/ run/ root/ var/ vmlinuz.old lib64/ boot/ 
sys/ 
    srv/ etc/ vmlinuz initrd.img.old usr/ lib/ sbin/ swapfile media/ home/ 
initrd.im
    g tmp/ proc/ mnt/

Good, `/` shows correct contents; `ls (md/root)/` shows the same. `ls /etc` 
also shows correct contents.
But:

    grub rescue> ls /boot

Empty! This is incorrect.

For a test, I also ran

    touch /mnt/testfile
    mkdir /mnt/testdir
    touch /mnt/testdir/testfile2

from Linux.
In GRUB2, `ls /` showed both `testfile` and `testdir`, but `ls /testdir/` 
showed no contents (`testfile2` was missing).

I also tried with xfs instead of ext4, in which case GRUB2 emits:

    error: not a correct XFS inode.
    error: not a correct XFS inode.
    error: not a correct XFS inode.
    error: not a correct XFS inode.
    error: not a correct XFS inode.
    error: not a correct XFS inode.
    error: not a correct XFS inode.
    error: not a correct XFS inode.
    error: file `/boot/grub/i386-pc/normal.mod' not found.
    Entering rescue mode...
    grub rescue>

When I do not make an 8 TB ext4/xfs file system, but use a small ext2 /boot 
partition, then GRUB2 works fine.

What is going on here?

Should GRUB2 be able to read from a single 8 TB ext4/xfs file system? Is this a 
bug?

Insights would be very appreciated.

Thank you,
Niklas