Nixos with raid-0 root partition using mdadm

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’).

# Download graphical ISO, http://nixos.org/nixos/download.html
# if you want to do an install over an SSH connection

# $ systemctl start sshd.service
# $ useradd remoteinstaller
# $ passwd remoteinstaller
# $ passwd root

# $ ssh remoteinstaller@<nix live cd host>
# $ su root

## create /dev/sda1 
# fdisk n p 1 <return> +50M 
## create /dev/sda2 /dev/sdb2 (do this on both disks)
# fdisk <disk> n p 2 <return> <return>
# mdadm --create /dev/md0 --level=0 --raid-devices=2 /dev/sda2 /dev/sdb2
# mkfs.ext4 -L boot /dev/sda1
# mkfs.ext4 -L nix /dev/md0
# mount -L nix /mnt
# nixos-generate-config --root /mnt

##  edit /mnt/nixos/configuration.nix to be like below
# $ nano /mnt/etc/nixos/configuration.nix

# then

# ** remove filesystem entry in **
# ** remove filesystem entry in **
#     vim /mnt/etc/nixos/hardware-configuration.nix
# else it will conflict with configuration.nix during `nixos-install`

# $ nixos-install

{ 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;
  # Define on which hard drive you want to install Grub.
  boot.loader.grub.device = "/dev/sda";

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

  # 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 by name, run:
  # $ nix-env -qaP | grep wget
  # environment.systemPackages = with pkgs; [
  #   wget
  # ];

  # List services that you want to enable:

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


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

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

  # Enable the KDE Desktop Environment.
  # services.xserver.displayManager.kdm.enable = true;
  # services.xserver.desktopManager.kde4.enable = true;

  # Define a user account. Don't forget to set a password with ‘passwd’.
  # users.extraUsers.guest = {
  #   isNormalUser = true;
  #   uid = 1000;
  # };

  # The NixOS release to be compatible with for stateful data such as databases.
  system.stateVersion = "16.03";

  fileSystems = {
    "/" = {
      device = "/dev/disk/by-label/nix";
      fsType = "ext4";
    };
    "/boot" = {
      device = "/dev/disk/by-label/boot";
      fsType = "ext4";
    };
  };

}