Placing a checkpoint on a coupling facility structure ensures equal access among MAS members and provides a better use of system resources than that available through DASD. Data can be transferred to and from a coupling facility much faster than to and from DASD.

JES2 uses the coupling facility lock to serialize access to the checkpoint data set. This coupling facility lock is better than the hardware RESERVE and RELEASE macros required for DASD because it ensures all members fair access to the checkpoint through first-in, first-out (FIFO) queuing. The coupling facility lock affects only the checkpoint data set, while the hardware RESERVE macro locks the entire volume upon which the DASD checkpoint resides.