Data is transferred along the data path from the bidirectional ports on the primary storage system to the bidirectional ports on the secondary storage systems. The amount of data each of these ports can transfer is limited.
Therefore, you must know the amount of data that will be transferred (that is, the write-workload) during peak periods. You can then ensure that bandwidth meets data transfer requirements, that the primary storage system has a sufficient number of bidirectional ports, and that the secondary storage system has a sufficient number of bidirectional ports to handle peak workload levels.