  In the mirror world hypothesis the mirror baryonic component emerges as a
possible dark matter candidate. An immediate question arises: how the mirror
baryons behave and what are the differences from the more familiar dark matter
candidates as e.g. cold dark matter? In this paper we answer quantitatively to
this question. First we discuss the dependence of the relevant scales for the
structure formation (Jeans and Silk scales) on the two macroscopic parameters
necessary to define the model: the temperature of the mirror plasma (limited by
the Big Bang Nucleosynthesis) and the amount of mirror baryonic matter. Then we
perform a complete quantitative calculation of the implications of mirror dark
matter on the cosmic microwave background and large scale structure power
spectrum. Finally, confronting with the present observational data, we obtain
some bounds on the mirror parameter space.
