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 receiving a plurality of data writes while being in the first data transfer mode, the primary storage device associating data writes begun after a first time and before a second time with a first chunk of data, the primary storage device associating data writes begun after the second time with a second chunk of data different from the first chunk of data, and the primary storage device transitioning to the second data transfer mode after the second time by first transferring writes associated with the 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 the second chunk of data to the secondary storage device using the first data transfer mode, where writes begun after initiating transitioning are provided to the secondary storage device using the second data transfer mode. Transitioning from a first data transfer mode to a second data transfer mode that is different from the first data transfer mode may also include, following the primary storage device transferring all writes associated with the first chunk of data to the secondary storage device, the primary storage device sending a message to the secondary storage device, and, in response to receiving the message from the primary storage device, the secondary storage device storing the data writes associated with the first chunk of data.