1. A system for replicating changes to data stored on a portable device to a data target, the system comprising: a change tracking component configured to, when the portable device is not communicatively coupled to the data target: receive an indication of a detected change to data stored in a data store of the portable device; and in response to the indication, store information in a data structure that indicates the detected change to the data, wherein the data store has blocks having sizes and the data structure is a bitmap, and wherein each bit of the bitmap is associated with a block of data stored in the data store, and the size of each block is determined based on a size limit of the bitmap; and a change replication component configured to, when the portable device is communicatively coupled to the data target: receive an indication that the portable device is communicatively coupled to the data target; in response to the indication, access the information stored in the data structure; and copy the change to the data indicated by the information to the data target.