{
  # ==================================================================
  #
  # Tool for creating snapshots and remote backups of btrfs subvolumes
  #   https://github.com/digint/btrbk
  #
  # Usage:
  #   1. btrbk will create snapshots on schedule
  #   2. we can use `btrbk run` command to create a backup manually
  #
  # How to restore a snapshot:
  #   1. Find the snapshot you want to restore in /snapshots
  #   2. Use `btrfs subvol delete /btr_pool/@persistent` to delete the current subvolume
  #   3. Use `btrfs subvol snapshot /snapshots/2021-01-01 /btr_pool/@persistent` to restore the snapshot
  #   4. reboot the system or remount the filesystem to see the changes
  #
  # ==================================================================

  services.btrbk.instances.btrbk = {
    # How often this btrbk instance is started. See systemd.time(7) for more information about the format.
    onCalendar = "daily";
    settings = {
      # keep daily snapshots for 14 days
      snapshot_preserve = "14d";
      # keep all snapshots for 2 days, no matter how frequently you (or your cron job) run btrbk
      snapshot_preserve_min = "2d";
      volume = {
        "/btr_pool" = {
          subvolume = {
            "@persistent" = {
              snapshot_create = "always";
            };
          };
          target = "/snapshots";
        };
      };
    };
  };
}