# File lib/ole/storage/base.rb, line 604
      def initialize bat, mode='r', params={}
        mode, params = 'r', mode if Hash === mode
        first_block, size = params.values_at :first_block, :size
        raise ArgumentError, 'must specify first_block' unless first_block
        @bat = bat
        self.first_block = first_block
        # we now cache the blocks chain, for faster resizing.
        @blocks = @bat.chain first_block
        super @bat.io, mode, :ranges => @bat.ranges(@blocks, size)
      end