nixos-servers/nixos/modules/storage.nix

{ lib, config, machine, ... }:
let cfg = config.lab.storage;
in {
  options.lab.storage = {
    osDisk = lib.mkOption {
      type = lib.types.str;
      description = ''
        The disk to be used for the machine's operating system.
      '';
    };

    dataPartition = lib.mkOption {
      type = lib.types.str;
      description = ''
        Partition to be used for data storage on this machine.
      '';
    };

    dataMountPoint = lib.mkOption {
      default = "/mnt/data";
      type = lib.types.str;
      description = ''
        Mount point of the machine's data partition.
      '';
    };
  };

  config = lib.mkIf (machine.type == "physical") {
    fileSystems.${cfg.dataMountPoint}.device = cfg.dataPartition;

    # TODO: Rename this to 'osDisk'. Unfortunately, we would need to run nixos-anywhere again then.
    disko.devices.disk.vdb = {
      device = cfg.osDisk;
      type = "disk";

      content = {
        type = "gpt";

        partitions = {
          swap.size = "100%";

          ESP = {
            type = "EF00";
            size = "500M";

            content = {
              type = "filesystem";
              format = "vfat";
              mountpoint = "/boot";
            };
          };

          root = {
            end = "-4G";

            content = {
              type = "filesystem";
              format = "btrfs";
              mountpoint = "/";
            };
          };
        };
      };
    };
  };
}