If a system failure occurs after a checkpoint has been taken, the automatic restart will occur at the last checkpoint if you have specified RD=R (or omitted the RD parameter) in the EXEC or JOB statement.
If a system failure occurs before any checkpoint has been taken, an automatic restart, from the beginning of the job step, can still occur if you have specified RD=R in the EXEC or JOB statement.
After a system failure occurs, you can still force automatic restart from the beginning of the job step by specifying RD=RNC in the EXEC or JOB statement. By specifying RD=RNC, you are requesting an automatic step restart without checkpoint processing if another system failure occurs.