A computer-implemented method includes receiving a source data set and a target data set. Differences between the target data set and the source data set are identified by dividing the target data set into a set of target data blocks. At least one duplicate block that is identical to a first portion of the source data set is identified among the target data blocks. At least one modified block for which contents of the modified block are not duplicated within the source data set is identified among the target data blocks. Different portions and identical portions between the modified block and the source data set are also identified.