In synchronous mode (SRDF/S), the primary array waits until the secondary array has acknowledged each write before the next write is accepted, ensuring that the replicated copy of the data is always as current as the primary. However, the latency due to propagation increases significantly with distance. Asynchronous SRDF (SRDF/A) transfers changes made to the secondary array in units called delta sets, which are transferred at defined intervals. Although the remote copy of the data will never be as current as the primary copy, this method can replicate data over considerable distances and with reduced bandwidth requirements and minimal impact on host performance.
Hi Team,  please help me by providing the major difference between SRDF/S and SRDF/A.  and also please let know on which situation thease two are used. 
Difference between SRDF Synchronous and SRDF Asynchronous