hendrik:
> Currently booting from a 750G BIOS-partitioned disk.
> Trying to enable booting from the 4.7T drive, which is GPT partitioned.
>
> With grub-install I get errors:
>
> april:/farhome/hendrik# grub-install /dev/sda
> Installing for i386-pc platform.
> grub-install: warning: this GPT partition label contains no BIOS Boot Partition; embedding won't be possible.
> grub-install: error: embedding is not possible, but this is required for RAID and LVM install.
> april:/farhome/hendrik#
>
> Evidently there is some kind of incompatibility here.
>
> What is going on? What can I to do other than continuing to boot from
> small BIOS disks?

I have:

# file -s /dev/sda
/dev/sda: DOS/MBR boot sector, LInux i386 boot LOader; partition 1 : ID=0xee, start-CHS (0x0,0,1), end-CHS (0x3ff,254,63), startsector 1, 4294967295 sectors
# fdisk -l /dev/sda
Disk /dev/sda: 2.7 TiB, 3000592982016 bytes, 5860533168 sectors
Disk model: TOSHIBA MG03ACA3
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 7A22F348-BA09-4E8C-9EE5-D2534E719D7C

Device          Start        End    Sectors   Size Type
/dev/sda1        2048     194559     192512    94M Linux RAID
/dev/sda2      194560    1953791    1759232   859M Linux RAID
/dev/sda3     1953792   19531775   17577984   8.4G Linux RAID
/dev/sda4    19531776  117186559   97654784  46.6G Linux RAID
/dev/sda5   117186560  136718335   19531776   9.3G Linux RAID
/dev/sda6   136718336 1953124351 1816406016 866.1G Linux RAID
/dev/sda7  1953124352 5860532223 3907407872   1.8T Linux RAID
#

Using lilo and mdraid mirrored partitions, no problems at all.
I always use a small /boot partition first, no initrd, self compiled
kernel.

Hope this helps you.