Blockset sorting performance can be improved by using Hiperspace along with disk for temporary storage.

The HIPRMAX parameter sets the maximum amount of Hiperspace to be used during a run. Specifying HIPRMAX=OPTIMAL allows DFSORT to optimize the maximum amount of Hiperspace to be used during a run, subject to other system and concurrent Hipersorting, memory object sorting and dataspace sorting activity throughout the run. Total Hipersorting activity on a system can be further limited by the EXPMAX, EXPOLD, and EXPRES installation options. See the description of HIPRMAX in OPTION control statement for more information.