https://www.ibm.com/docs/en/ims/15.4.0?topic=set-dfsspmxx-member-ims-proclib-data
IMS 15.4 - System definition - DFSSPMxx member of the IMS PROCLIB data set
Use the DFSSPMxx member of the IMS PROCLIB data set to override the default buffer definitions for the storage pools managed by the DFSPOOL storage manager.