A drive subset matrix is created with at least N+1 drives each having N*N same-size subdivisions. Conceptually, N submatrices are created along with spares equivalent to at least one drive of storage capacity. The spares are located such that every drive has an equal number of spares +/−1. One protection group is located in a lowest indexed subdivision of each of the submatrices. Members of other protection groups are located by selecting members in round robin order and placing each selected member in a free subdivision having a lowest drive index and lowest subdivision index. The drive subset can be grown, split, and reorganized to restore balanced and efficient distribution of spares.