Embodiments of the present disclosure provide a method, apparatus and computer program product for data backup. A method includes obtaining first information about data change in a virtual disk, where the first information indicates that data in at least one block of a plurality of blocks is changed. The method also includes determining, based on the first information, second information about a location of the at least one block in the virtual disk. The method further includes obtaining a first size of the virtual disk backed up to a backup server prior to the data change and a second size of the virtual disk subsequent to the data change. In addition, the method includes generating, based on the second information, the first size and the second size, incremental backup data for backing up the virtual disk having the second size to the backup server.