why it's not possible to boot from a HDD larger than 4TB

[Amen8]

i came to this conclusion after so many tests
and it's really a sad reality
am not sure about Raspberry-OS because i dont even care to test it.
so here is what i have done:
1- I partitionned my HDD using GPT tables, because that's the only way to make partitions larger than 2TB
first partition has 256Mb labeled system-boot, the second one has 600Gb and I labeled it writable
and for the rest of my 8TB drive I devided by 2 (approximatly 3,5TB each)
2- I burned the ubuntu image (replaced the *.elf and *.dat files then extracted vmlinuz to vmlinux, and my rpi's eeprom is already updated to support usb boot)
after burning the image I double checked the partitions and they were still as planned to be.
3- THE MOMENT I PLUG THE HDD TO MY RASPBERRY MACHINE AND TURN IT ON. THE DAMN PARTITIONS CHANGE !
I end up with the 256Mb system-boot partition
and the writable partitions is AUTOMATICALLY resized to 2TB. with the rest of the drive unallocated
if I try to change that. it wont allow me to. because surprisingly the GPT tables is coverted (without losing data) and the max partition size is now 2TB with a maximum partitions number of 4.
so I can only make 256Mb 600Gb then 2TB and another 2TB.
for the rest ? gone unallocated and cant be used
I just wonder why the hell my disk is no longer GPT partitionned and why the writable partition got resized

[pidd]

Did you leave non-partitioned space at the beginning and end of the drive for the GTP primary and secondary tables?

[cleverca22]

3- THE MOMENT I PLUG THE HDD TO MY RASPBERRY MACHINE AND TURN IT ON. THE DAMN PARTITIONS CHANGE !
I end up with the 256Mb system-boot partition
and the writable partitions is AUTOMATICALLY resized to 2TB. with the rest of the drive unallocated

that might be a bug in the auto-expand script?

what does `fdisk -l /dev/sdX` report for the disk, before you boot it?

[jamesh]

am not sure about Raspberry-OS because i dont even care to test it.

So don't expect Raspberry Pi engineers to help. You'll need to talk to the Ubuntu people.