Systems and methods for expanding capacity of a storage system are provided. Data blocks of a capacity increasing disk are pre-configured with a first progress indicator used to determine correctly migrated data blocks. A migrator migrates groups of data blocks among present disk(s) and capacity increasing disk(s). Each group comprises a predetermined number of data blocks. An updater updates a second progress indicator of the second disk in response to completion of migration of each group. The migrator is adapted to generate the first progress indicator such that it may resume migration of groups of data blocks after a migration interruption according to the first and the second progress indicators.