Unable to boot BIOS/GPT system.

[Daniel Fishman <quantera@gmail.com>]

Hello,

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.


Following are a bit more details about the partitions:

I used the following command to partition the HDD:

parted -s /dev/sdb mklabel gpt mkpart BIOS_boot ext2 1MiB 2MiB \
  mkpart swap linux-swap 2MiB 16000MiB mkpart data ext2 16000MiB 100% \
  set 1 bios_grub

[root@arch]# parted /dev/sdb unit MiB print
Model: WD Elements 25A1 (scsi)
Disk /dev/sdb: 3815415MiB
Sector size (logical/physical): 512B/4096B
Partition Table: gpt
Disk Flags:

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


Debian's installation was done on x64 BIOS-only system.