Assemble all mdadm disk arrays that are found if needed
mdadm --assemble --scan
Mount the desired server root file system
sudo mount /dev/sda1 /mnt/srvroot # Where /sda1 is an empty EFI formatted partition (VFAT, type=EFI)
Mount all system directories that are needed for the GRUB installation process
sudo mount -t /boot/efi /mnt/srvroot/boot/efi
sudo mount -t proc /proc /mnt/srvroot/proc/
sudo mount --rbind /sys /mnt/srvroot/sys/
sudo mount --rbind /dev /mnt/srvroot/dev/
sudo chroot /mnt/srvroot
Now continue with the EFI install guide