Re: Unable to boot BIOS/GPT system.
- Date: Fri, 23 Nov 2018 00:03:20 +0100
- From: Pascal Hambourg <pascal@xxxxxxxxxxxxxxx>
- Subject: Re: Unable to boot BIOS/GPT system.
Le 22/11/2018 à 20:19, Steve McIntyre a écrit :
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.