Abstract: A backup operation is performed on a source data set. The data set is segmented into a plurality of blocks. An update bit indicator is implemented for each of the plurality of blocks. The update bit indicator is appended to a field of an existing data index or tied to a mapping table having a relative byte address (RBA). The update bit indicator is set for each of the plurality of blocks which are newly created or changed from a first backup to a second backup, which generates a dump data set containing compressed blocks from the source data set. A backup operation is executed to backup each of the plurality of blocks having the update bit indicator set. The data index or mapping table is updated to show which of the plurality of blocks have changed from the first backup to the second backup.