nixos-servers/nixos/modules/storage.nix

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

    dataPartition = lib.mkOption {
      default = null;
      type = lib.types.nullOr 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 = {
    fileSystems = lib.attrsets.mergeAttrsList [
      (lib.optionalAttrs machine.isHypervisor {
        "${cfg.dataMountPoint}".device = cfg.dataPartition;
      })
      (lib.optionalAttrs machine.isRaspberryPi {
        "/" = {
          device = "/dev/disk/by-label/NIXOS_SD";
          fsType = "ext4";
          options = [ "noatime" ];
        };
      })
    ];

    disko = lib.mkIf machine.isHypervisor {
      # TODO: Rename this to 'osDisk'. Unfortunately, we would need to run nixos-anywhere again then.
      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 = "/";
              };
            };
          };
        };
      };
    };
  };
}