A method for storing inventory items in an inventory system includes receiving a replenish request identifying an inventory item to be stored in an inventory system and determining a classification of the inventory item to be stored. The method also includes selecting an inventory holder from a plurality of inventory holders based, at least in part, on the classification of the inventory item to be stored and a classification of one or more other inventory items currently stored in the selected inventory holder. Additionally, the method includes transmitting information identifying the selected inventory holder to a mobile drive unit.