  Zariski decomposition is a fundamental tool for studying linear systems of
divisors on algebraic surfaces. Bauer, K\"uronya and Szemberg obtained a
decomposition of the big cone of a smooth projective surface into chambers,
called Zariski chambers, in each of which the support of the negative part of
the Zariski decomposition is constant. On the other hand, thanks to the work of
Boucksom, on a compact complex manifold we have the divisorial Zariski
decomposition which, on an irreducible holomorphic symplectic manifold (IHS),
is a higher dimensional Zariski decomposition with respect to the
Beauville-Bogomolov-Fujiki quadratic form. Similarly to the case of surfaces,
we provide for the big cone of a projective irreducible holomorphic symplectic
manifold a decomposition into chambers (which we describe in detail), in each
of which the support of the negative part of the divisorial Zariski
decomposition is constant. As for surfaces, the obtained decomposition of the
big cone allows to describe the volume function, which turns out to behave very
well. Moreover, always inspired by the surface case, we also see that the big
cone of a projective IHS manifold admits a decomposition into simple Weyl
chambers, which we compare to that induced by the divisorial Zariski
decomposition. To conclude, we investigate the boundary of the big cone and
determine the structure of the algebraic pseudo-effective cone.
