---

fileSystems."/" = {
    device = "/dev/sda2";
    fsType = "btrfs";   # или ext4 — посмотри по lsblk -f
  };

  fileSystems."/boot" = {
    device = "/dev/sda1";
    fsType = "vfat";
  };

  swapDevices = [ { device = "/dev/sda3"; } ];