To process objects greater than 256MB in the file system sublevel or on tape, the OAM address space uses 64–bit addressing and virtual storage above the 2G bar. Additional configuration may be required to specify a MEMLIMIT value that will provide virtual storage above the 2G bar to the OAM address space. Typically specifying REGION=0M on the OAM started procedure JCL implies a MEMLIMIT value that provides the OAM address space with the needed virtual storage above the 2G bar. This REGION=0M specification is recommended to avoid issues with virtual storage shortages and is the default in the sample OAM procedure. See 5h Updating the PROCLIB.

The MEMLIMIT value can be explicitly set or implicitly provided in a number of different ways and can be overridden by an installation exit, so you must ensure the resulting MEMLIMIT specification is sufficient for OAM. For more information on MEMLIMIT, see z/OS Migration and z/OS MVS Programming: Extended Addressability Guide.

OAM usage of virtual storage above the 2G bar will result in significantly increased storage utilization on your system. For more information see Auxiliary storage and real storage considerations and System paging.