Determining maximum drive capacity for RAID-5 allocation in a virtualized storage pool

Methods of determining the maximum storage capacity in a storage system that implements RAID-5 redundancy are described. In one implementation the method comprises determining a chunk size of addressable physical storage segments available for allocation in a redundant storage set comprising a plurality of physical disk drives; determining a number of redundant storage units per disk using the chunk size; determining a disk contribution value for each disk in the storage set; and allocating physical storage segments on the plurality of physical drives in accordance with the disk contribution value.