When you create a ShadowImage for Mainframe pair, the storage system performs an initial copy operation to copy the data in the P-VOL to the S-VOL. You can create a pair and then immediately split the pair to gain access to the S-VOL.
When you create a ShadowImage for Mainframe pair, the MP unit assigned to the P-VOL is also assigned as the MP unit for the S-VOL.