To improve the performance of DataStage jobs, you should first define the baselines. Secondly, try using multiple flows for performance testing. Then start working in increments. Now, evaluate the data skews. Now you should isolate and solve the problem one by one. This is the time for distributing file systems to remove bottlenecks. RDBMS should not be used in the beginning. In the ned, you should understand and assess the available tuning knobs.