When you create a pair, the storage system performs an initial copy to copy data in the P-VOL to the S-VOL. You can create the SI pair and immediately split the pair so that you can access the S-VOL. You can also create a cascaded pairs.
Creating an SI pair causes the MP unit that is responsible for processing the P-VOL LDEV's I/O to assume processing responsibility for the S-VOL LDEV's I/O operations.