1. A computer program embodied on a computer readable medium, comprising: program instructions for allocating a plurality of backup LUNs identified in a backup management file from a plurality of available LUNs identified in a universe file such that the backup management file identifies a plurality of data containers currently available for backup, where each of the plurality of the data containers in the backup management file specifies a subset comprising more than one of the plurality of backup LUNs, the subset being currently capable of backing up a dataset, the dataset being stored on a plurality of used dataset LUNs, and the universe file identifies the plurality of available LUNs for use in a current backup; and program instructions for allocating one of the plurality of data containers for the current backup of the dataset; wherein allocating the plurality of backup LUNs comprises querying the dataset comprising the plurality of used dataset LUNs to determine a dataset size of the plurality of used dataset LUNs and allocating the plurality of backup LUNs based on the dataset size and a backup size of each of the available LUNs used in the context of storage subsystem rules for matching to create each of the plurality of the data containers identified in the backup management file.