The private (24-bit) and extended private (31-bit) address space requirements for DFSMShsm are dynamic. DFSMShsm’s region size should normally default to the private virtual address space (REGION=0).

To run ABARS processing, each secondary address space for aggregate backup or aggregate recovery requires 4MB. One megabyte of this ABARS secondary address space is above the line (in 31-bit extended private address space). The other 3MB are below the line (in 24-bit address space).

As you add more functions and options to the DFSMShsm base product, the region-size requirement increases. You should therefore include the maximum region size in your setup procedure.