Support to install debian RAID1 UEFI

I ve 2 one TB hard drive. Uefi mode installation needs more partition than bios mode. I tried with / root directory 984 GB (2times) and swap partition 16 GB (2times) . Disk partition warning: it might be difficult to reboot the machine into any bios-mode operation system later. Question: is it normal warning or am missing any essential partition /boot/efi fat32 etc ?