Configuration

This section will cover a few system-level configurations you can make to improve performance.

Nix storage optimisations

You may find that Nix uses quite a large amount of storage space. This is simply how it works. See garbage collection.

This enables automatic garbage collection. One may change the options to --delete-old to delete everything other than the current generation.

/etc/nixos/configuration.nix
nix.gc = {
automatic = true;
dates = "weekly";
options = "--delete-older-than 7d";
};

The next optimisation is to replace identical files in the store with hard links. There is no need to run this very often.

/etc/nixos/configuration.nix
nix.optimise = {
automatic = true;
dates = [ "weekly" ];
};

Power optimisations

Below are a few optimisations. Perhaps the biggest one is to enable powertop's automatic configuration. A good resource is the Arch wiki on power management.

/etc/nixos/configuration.nix
boot.kernel.sysctl = {
  "kernel.nmi_watchdog" = 0;
  "vm.dirty_writeback_centisecs" = 6000;
  "vm.laptop_mode" = 5;
};

powerManagement = {
  powertop.enable = true;
  scsiLinkPolicy = "med_power_with_dipm";
};

If you want your disks to spin down, you can also configure hdparm:

/etc/nixos/configuration.nix
powerManagement.powerUpCommands = ''
${pkgs.hdparm}/sbin/hdparm -S 242 /dev/sda
${pkgs.hdparm}/sbin/hdparm -S 242 /dev/sdb
${pkgs.hdparm}/sbin/hdparm -S 242 /dev/sdc
'';

# etc.

The value 242 is actually a full hour. You may want to visit man hdparm regarding how this value is calculated.