{ ... }:
{
  systemd.tmpfiles.rules = [
    "d /persist/user.bak 0755 root root"
    "d /persist/state.bak 0755 root root"
  ];

  services.btrbk = {
    ioSchedulingClass = "idle";
    niceness = 19;
    instances = {
      persist-user = {
        onCalendar = "hourly";
        settings.volume."/persist" = {
          subvolume = "user";
          snapshot_dir = "user.bak";
          snapshot_preserve_min = "latest";
          snapshot_preserve = "48h 14d 4w 6m";
        };
      };

      persist-state = {
        onCalendar = "daily";
        settings.volume."/persist" = {
          subvolume = "state";
          snapshot_dir = "state.bak";
          snapshot_preserve_min = "latest";
          snapshot_preserve = "7d 4w 3m";
        };
      };
    };
  };
}