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Re: Unable to boot BIOS/GPT system.

Le 22/11/2018 à 20:19, Steve McIntyre a écrit :
quantera@xxxxxxxxx wrote:

I am trying to install Debian on a 4TB external HDD. Since I want
to boot the HDD (also) on old systems which support only BIOS,
and since the HDD is larger than 2TB, I decided to go with GPT
partition table and BIOS boot (or, in other words: BIOS/GTP).
I partitioned the HDD accordingly (see the details below), and
installed Debian. During a pre-installation configuration the
installer recognized BIOS boot partition, I configured the root
partition as ext4 and installed grub into the disk's MBR. But
when (after an installation) I am trying to boot the HDD, I receive
an error message: 'error: unknown filesystem' and drop into a
grub rescue mode.

What is the problem here and how it can be solved? It seems as
though grub's Stage 1.5 loader (that is - core.img, which is
supposed to be embedded in BIOS boot partition) doesn't contain
modules needed to read ext4 filesystem, which seems very strange.


Number  Start     End         Size        File system     Name  Flags
  1      1.00MiB   2.00MiB     1.00MiB                           bios_grub
  2      2.00MiB   16000MiB    15998MiB    linux-swap(v1)
  3      16000MiB  3815414MiB  3799414MiB

I'd expect that Grub won't be able to reliably work with that setup -
partition 3 goes past the 2TB mark, so the BIOS won't be able to map
it properly. Don't forget, when grub is reading the disk all it can
rely on are BIOS calls. Add yourself a small-ish /boot partition first
and you may be OK.

The limit of EDD BIOS calls which uses 64 bit LBA addressing is way beyond 2 TiB. But that specific BIOS implementation may be broken and unable to read beyond that limit. So indeed a boot or root partition at the beginning of the disk may help.