blkid output

/dev/sdb1: UUID="1970-01-01-00-00-01-00" LABEL="NIXOS_ISO" TYPE="iso9660" PTUUID="c8e0e6ee" PTTYPE="dos" PARTUUID="c8e0e6ee-01"
/dev/loop0: TYPE="squashfs"
/dev/sda1: UUID="85E2-F536" TYPE="vfat" PARTLABEL="EFI System" PARTUUID="37ae1336-a652-43fd-a853-4b254e9abaef"
/dev/sda2: UUID="78c53c41-1379-4bc3-9990-527fd6232ca1" TYPE="crypto_LUKS" PARTLABEL="Linux filesystem" PARTUUID="f7983a37-e4b8-4287-ad6f-4a249c90b9d6"
/dev/sdb2: SEC_TYPE="msdos" LABEL_FATBOOT="EFIBOOT" LABEL="EFIBOOT" UUID="1234-5678" TYPE="vfat" PARTUUID="c8e0e6ee-02"
/dev/mapper/crypted-nixos: UUID="BB6RmT-B4Wy-hflm-BtXb-lyxL-Xmq6-SSgXhF" TYPE="LVM2_member"
/dev/mapper/vg-swap: LABEL="swap" UUID="3e0b6cc7-e28c-45ff-99e6-620a1441dacd" TYPE="swap"
/dev/mapper/vg-root: LABEL="root" UUID="87ba2cd8-d13e-4c6d-b114-355133a674bc" TYPE="ext4"

configuration.nix

# Edit this configuration file to define what should be installed on
# your system.  Help is available in the configuration.nix(5) man page
# and in the NixOS manual (accessible by running ‘nixos-help’).

{ config, pkgs, ... }:

{
  imports =
    [ # Include the results of the hardware scan.
      ./hardware-configuration.nix
    ];

  # Use the GRUB 2 boot loader.
  #boot.loader.grub.enable = true;
  #boot.loader.grub.version = 2;
  # boot.loader.grub.efiSupport = true;
  # boot.loader.efi.efiSysMountPoint = "/boot/efi";
  # Define on which hard drive you want to install Grub.
  # boot.loader.grub.device = "/dev/sda"; # or "nodev" for efi only
  boot.loader.efi.canTouchEfiVariables = true;
  boot.loader.efi.efiSysMountPoint = "/boot/efi";
  boot.loader.grub = {
    efiInstallAsRemovable = true;
    enable = true;
    device = "nodev";
    version = 2;
    efiSupport = true;
    enableCryptodisk = true;
    extraInitrd = /boot/initrd.keys.gz;
  };

  boot.initrd.luks.devices = [
      {
        name = "root";
        device = "dev/disk/by-uuid/78c53c41-1379-4bc3-9990-527fd6232ca1"; 
        preLVM = true;
        keyFile = "/keyfile0.bin";
        allowDiscards = true;
      }
  ];

  # networking.hostName = "nixos"; # Define your hostname.
  # networking.wireless.enable = true;  # Enables wireless support via wpa_supplicant.

  # Configure network proxy if necessary
  # networking.proxy.default = "http://user:password@proxy:port/";
  # networking.proxy.noProxy = "127.0.0.1,localhost,internal.domain";

  # Select internationalisation properties.
  # i18n = {
  #   consoleFont = "Lat2-Terminus16";
  #   consoleKeyMap = "us";
  #   defaultLocale = "en_US.UTF-8";
  # };

  # Set your time zone.
  # time.timeZone = "Europe/Amsterdam";

  # List packages installed in system profile. To search, run:
  # $ nix search wget
  # environment.systemPackages = with pkgs; [
  #   wget vim
  # ];

  # Some programs need SUID wrappers, can be configured further or are
  # started in user sessions.
  # programs.mtr.enable = true;
  # programs.gnupg.agent = { enable = true; enableSSHSupport = true; };

  # List services that you want to enable:

  # Enable the OpenSSH daemon.
  # services.openssh.enable = true;

  # Open ports in the firewall.
  # networking.firewall.allowedTCPPorts = [ ... ];
  # networking.firewall.allowedUDPPorts = [ ... ];
  # Or disable the firewall altogether.
  # networking.firewall.enable = false;

  # Enable CUPS to print documents.
  # services.printing.enable = true;

  # Enable sound.
  # sound.enable = true;
  # hardware.pulseaudio.enable = true;

  # Enable the X11 windowing system.
  # services.xserver.enable = true;
  # services.xserver.layout = "us";
  # services.xserver.xkbOptions = "eurosign:e";

  # Enable touchpad support.
  # services.xserver.libinput.enable = true;

  # Enable the KDE Desktop Environment.
  # services.xserver.displayManager.sddm.enable = true;
  # services.xserver.desktopManager.plasma5.enable = true;

  # Define a user account. Don't forget to set a password with ‘passwd’.
  # users.users.jane = {
  #   isNormalUser = true;
  #   extraGroups = [ "wheel" ]; # Enable ‘sudo’ for the user.
  # };

  # This value determines the NixOS release with which your system is to be
  # compatible, in order to avoid breaking some software such as database
  # servers. You should change this only after NixOS release notes say you
  # should.
  system.stateVersion = "19.03"; # Did you read the comment?

}

hardware-configuration.nix

# Do not modify this file!  It was generated by ‘nixos-generate-config’
# and may be overwritten by future invocations.  Please make changes
# to /etc/nixos/configuration.nix instead.
{ config, lib, pkgs, ... }:

{
  imports =
    [ <nixpkgs/nixos/modules/installer/scan/not-detected.nix>
    ];

  boot.initrd.availableKernelModules = [ "xhci_pci" "ehci_pci" "ahci" "usb_storage" "sd_mod" "sdhci_pci" ];
  boot.initrd.kernelModules = [ "dm-snapshot" ];
  boot.kernelModules = [ "kvm-intel" ];
  boot.extraModulePackages = [ ];

  fileSystems."/" =
    { device = "/dev/disk/by-uuid/87ba2cd8-d13e-4c6d-b114-355133a674bc";
      fsType = "ext4";
    };

  fileSystems."/boot/efi" =
    { device = "/dev/disk/by-uuid/85E2-F536";
      fsType = "vfat";
    };

  swapDevices =
    [ { device = "/dev/disk/by-uuid/3e0b6cc7-e28c-45ff-99e6-620a1441dacd"; }
    ];

  nix.maxJobs = lib.mkDefault 4;
  powerManagement.cpuFreqGovernor = lib.mkDefault "powersave";
}

mount output

/dev/mapper/vg-root on /mnt type ext4 (rw,relatime)
/dev/sda1 on /mnt/boot/efi type vfat (rw,relatime,fmask=0022,dmask=0022,codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro)