The quantum Hall ferromagnets at the half-filling of a pair of degenerateelectron or composite fermion Landau levels are studied by exact numeri-cal diagonalization. The results obtained using open and closed geometries(rectangular — with periodic boundary conditions and spherical) are com-pared. The ferro- and paramagnetic ground states are identified in finite-sizeenergy spectra, and the pair-correlation functions are used in search of thedomain structure at half-polarization.