15. A computer program product for data storage management, the computer program product comprising: a non-transitory, computer-readable storage medium; and computer-readable program code embodied in the storage medium, wherein the computer-readable program code is configured to determine, for each leaf storage space of a data storage space hierarchy having at least two leaf storage spaces descending from at least one summary storage space, wherein each leaf storage space has at least one attribute type, an invariant leaf storage space attribute value for each attribute type of the leaf storage space; determine, for each summary storage space, an invariant summary storage space attribute value for each attribute type of each leaf storage space descending from the summary storage space as a sum of the invariant leaf storage space attribute values of all leaf storage spaces descending from the summary storage space; determine, for each leaf storage space, a variable leaf storage space attribute value for each attribute type of the leaf storage space; and determine, for each summary storage space, a variable summary storage space attribute value for each attribute type of each leaf storage space descending from the summary storage space, wherein for each summary storage space, and for each storage space immediately descending from the summary storage space, each variable leaf storage space attribute value of the immediately descending storage space is expressed as a proportion of the variable summary storage space attribute value of the summary storage space for the same attribute type.
16. The computer program product of claim 15 wherein the wherein the data storage space hierarchy is embodied in a magnetic or optical data storage device.