Since all SAP jobs run by default in the*BASE pool (system pool 2), you should make as much memory as possible available for this pool. 400 MB is the absolute minimum. If you still have other applications running on your iSeries system, assign a separate pool to the SAP System.
Minimum memory for pool 2: 400 MB
See also:Main Storage Pools (iSeries)Checking Page Fault Rates (iSeries)