class Lumberjack::Device::SizeRollingLogFile

def initialize(path, options = {})

the :max_size option. The unit can also be specified: "32K", "100M", "2G" are all valid.
Create an new log device to the specified file. The maximum size of the log file is specified with 
def initialize(path, options = {})
  @manual = options[:manual]
  @max_size = options[:max_size]
  if @max_size.is_a?(String)
    if @max_size =~ /^(\d+(\.\d+)?)([KMG])?$/i
      @max_size = $~[1].to_f
      units = $~[3].to_s.upcase
      case units
      when "K"
        @max_size *= 1024
      when "M"
        @max_size *= 1024**2
      when "G"
        @max_size *= 1024**3
      end
      @max_size = @max_size.round
    else
      raise ArgumentError.new("illegal value for :max_size (#{@max_size})")
    end
  end
  super
end