Storage arrays are subdivided into a plurality of physical and logical entities to provide a framework of the available storage. In a large SAN, the network of storage arrays may define a complex arrangement of such physical and logical entities to partition the total storage volume. Therefore, the storage area network classifies a series of storage categories corresponding to different levels of the physical and logical entities representing subdivisions of the storage. In the storage array, designated storage is often not immediately employed for storing active data. In the enumerated storage categories, storage is apportioned from the previous category level in a progressive manner. Storage utilization reports which simultaneously display a plurality of storage category levels, and compute designated and free storage capacity at each level, indicate underutilized or potential available storage which may be obscured by imprecise or overly generous storage allotment estimates. The storage categories therefore identify a manner in which the available storage area is allotted, or apportioned.