The SESSION option suspends all volume pairs in the XRC session when an error is associated with any duplex volume that has ERRORLEVEL(SESSION) specified. The system data mover (SDM) then continues to read the updates from the primary storage controls. It does not copy data to secondary volumes until you have added the volume pairs back to the session. You need to copy only the changed data when you add the volumes. You must correct the error condition and resynchronize the suspended volume pairs. If SESSION is selected and a failure occurs on a single storage control that attaches to any duplex volume pair with ERRORLEVEL(SESSION) specified, then all XRC volume pairs are put into suspended state. XRC suspends volume pairs that are in pending state, and the pairs remain where they are in synchronization. Software bitmapping continues for all volumes that are part of the XRC session. In addition, if the affected session is a coupled session, all volumes in all other coupled sessions that are associated with the same master session will also be suspended. The master session is placed into HOLD status to protect the recoverable time for each XRC session.