Transitioning from a first data transfer mode to a second data transfer mode that is different from the first data transfer mode includes a primary storage device transitioning to the second data transfer mode by first transferring writes associated with a first chunk of data to a secondary storage device after completion of all writes associated with the first chunk of data and then, after all writes associated with the first chunk of data have been transferred to the secondary storage device, transferring writes associated with a second chunk of data to the secondary storage device using the first data transfer mode. Writes begun after initiating transitioning are provided to the secondary storage device using the second data transfer mode.