1. A computer program product for performing deduplication for a storage, the computer program product comprising a computer readable storage having computer readable program code embodied therein that executes to perform operations, the operations comprising: maintaining an index of chunk signatures calculated from chunks of data in the data objects in the storage, wherein each index entry includes at least one of the chunk signatures and a reference to the chunk of data from which the signature was calculated; selecting entries in the index to merge; performing a merge operation on the chunk signatures in the selected entries to calculate a merged signature; adding an entry to the index including the merged signature and a reference to the chunks in the storage referenced in the merged selected entries; removing the selected entries used to calculate the merged signature from the index; and using the index of the signatures in deduplication operations when adding data objects to the storage.