[root@nixos:/mnt]# lsblk
NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT
loop0 7:0 0 1.8G 1 loop /nix/.ro-store
sda 8:0 0 119.2G 0 disk
├─sda1 8:1 0 1G 0 part /mnt/boot
├─sda2 8:2 0 40G 0 part
├─sda3 8:3 0 5G 0 part
├─sda4 8:4 0 600M 0 part /mnt/boot/efi
├─sda5 8:5 0 40G 0 part /mnt
└─sda6 8:6 0 2G 0 part [SWAP]
sdb 8:16 1 14.4G 0 disk
├─sdb1 8:17 1 1.8G 0 part /iso
└─sdb2 8:18 1 21M 0 part

boot.loader.grub.enable = true;
boot.loader.grub.efiSupport = true;
boot.loader.grub.device = "nodev";
boot.loader.efi.efiSysMountPoint = "/boot/efi";