Heterogeneous disk arrays are becoming a common configuration in many sites and specially in storage area networks (SAN). As new disks have different characteristics than old ones, adding new disks or replacing old ones ends up in a heterogeneous disk array. Current solutions to this kind of arrays do not take advantage of the improved characteristics of the new disks. In this paper, we present a block-distribution algorithm that takes advantage of these new characteristics and thus improves the performance and capacity of heterogeneous disk arrays compared to current solutions.