Effects of error situations when DUPLEX=OFF

The effects of an I/O error to your checkpoint data set can be disastrous:

If an I/O error occurs and the checkpoint volume becomes unavailable or damaged, you might be able to enter the checkpoint reconfiguration dialog from an active member of your MAS configuration and forward the data set to a new location.
If your member fails while losing the checkpoint volume and there are no other active members from your MAS configuration, you will lose all checkpointed data.

You can lessen the possibility of causing such a disruption to JES2 processing by defining a DUPLEX checkpoint data set and by adding the CKPT2= and DUPLEX=ON parameter specification to the CKPTDEF initialization statement. For an example of DUPLEX-mode processing with a backup, see DUPLEX-mode processing (with backup).

The complexity of DUAL processing is not required in a single-member environment.