Debian + 4TB SATA + md RAID - Grub won't install, or if it does, won't boot

Question

I'm trying to get Debian 7.8 amd64 setup on an system (G3220 CPU, mobo is an Asus H81I+) onto which I've installed two 4TB SATA hard drives.

I admit I'm not up to snuff on EFI and such.

My goal is to have a RAID1 25GB or so root (md0), 4GB of swap on each drive, and then the rest as one large data partition (md1, about 3.9TB).

My first attempt (using the guided partitioner and then modifying) was unsuccessful because grub would not install on /dev/sda - the installer gave a fatal error. Booting into rescue afterwards and entering root, then running grub-install gave a seg fault if I tried to grub-install to md0. Classy!

So I redid the install, this time making root a standalone ext4 partition. grub was successful, but at boot, there's a flashing cursor in the upper left for a couple moments and then it dumps me to BIOS.

Booted again into rescue and running grub-install /dev/sda gives "warn: Attempting to install GRUB to a partitionless disk or to a partition. This is a BAD idea..." and then an error with "error: will not proceed with blocklists".

Weirdly, /dev/sda2 is mounted as root and working.

The disks are partitioned with GPT (fdisk will give an error and partx prints the partition fine).

The BIOS is ASUS UEFO BIOS 2.10.1208.

There is a Compatibility Support Module that I have enabled. Settings are:

boot device control: UEFI and Legacy OPROM
boot from network device: UEFI driver first 
boot from storage devices: both, UEFI first
Boot from PCI-E: UEFI driver first (don't care about this)

I've tried with these settings, also with everything set to Legacy only or Legacy first.

There is a Secure Boot setting which is set to OS Type: Other OS (the other possibility is Windows UEFI Mode). SecureBoot is disabled (and shows that in the BIOS).

I admit I'm not very EFI/GPT savvy...what should I look at?

Do I need to redo the install using some sort of EFI setup? The installer chose a bios partition and created one.

This system ran OpenBSD for several months without any issue, thought with different (smaller) hard drives, which is why I'm suspicious it's something in the HDD setup.

Answer 1

You wrote:

There is a Compatibility Support Module that I have enabled.

Disable the CSM (aka legacy support or BIOS mode), then read up on installing Linux in EFI mode. My suspicion is that your problems stem from a BIOS-mode install on a 4TB disk. Some systems have problems with this because of GRUB and BIOS limitations; see for instance this Ubuntu bug report. (This bug is almost certainly not unique to Ubuntu, though; it's a limitation of GRUB and BIOS.) It could also be that your firmware just doesn't like using BIOS mode on over-2TiB disks.