Installer - add BIOS boot partition?

[Richard Hector <richard@walnut.gen.nz>]

Hi all,

I've just done most of an installation on a BIOS machine, with a pair of
new 4TB disks, which require GPT.

Grub fails to install, which I possibly should have predicted - though I
thought di might have either coped or warned me.

It seems I need a BIOS boot partition, and that it should fit in the
space before my first existing partition, is that right? Any tips on
creating such a thing, preferably from within the di environment?

Or do I need to do some partitioning before starting the installer?
Links to relevant references or howtos welcome.

Thanks,
Richard