A mechanism is provided for optimizing migration/copying of de-duplicated data from an internal storage system to a removable storage system. A preliminary number of clusters to be generated are determined for sets of data objects stored on the internal storage system based on a number of the sets of data objects. The preliminary number of clusters is generated based on shortest distances between the sets of data objects, each cluster comprising one or more sets of data objects and each set of data objects comprising one or more chunks of data. A chosen cluster is identified from a set of clusters by identifying a cluster having a greatest number of common chunks within as few sets of data objects. Responsive to an export-size of the chosen cluster failing to exceed the available storage capacity of the removable storage system, the chosen cluster is exported to the removable storage system.