1. A system for replicating changes to data stored on a portable device to an external data storage device, the system comprising: at least one processor; and, at least one data storage device coupled to the processor; wherein the processor is configured to— in response to an indication of a detected change to data stored in a data store of the portable device, 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, wherein data elements of the bitmap are associated with respective blocks of data stored in the data store, and wherein a size of each block is determined based on an existing threshold; and receive a connection indication that the portable device is communicatively coupled to the external data storage device; in response to the connection indication, access the information stored in the data structure; and copy the change to the data indicated by the information to the external data storage device.