What can I do with the unused shared area (24 bit) space ?
Ingolf24 120000DRN3 Comments (2) Visits (5947)
The shared area (24 bit) consists of the Supervisor, the Shared Virtual Area (SVA - 24 bit) and Shared Partitions (if allocated).
The SVA (24 bit) starts after the Supervisor area and consists of the System Directory List (SDL), Virtual Library Area (VLA), System GETVIS area (24 bit), System Label Work Area (SLA) and VPOOL. Shared Partitions are allocated after the SVA (24 bit). Non-shared (static and dynamic) partitions are allocated in the private area. The private area starts at the next one Megabyte (MB) boundary after the shared area (24 bit) as required by the z/Architecture.
The rounding to the one MB boundary may cause unused space in the shared area (24 bit), which cannot be allocated for any use after IPL complete. The MAP command output shows that unused space in the SVA-24 line in column "UNUSED". You may increase system resources e.g. via the IPL SVA command sizes (SDL, PSIZE, GETVIS), SYS command sizes (CHANQ, NPARTS), or the Supervisor parameter command sizes (IODEV, VPOOL), which reduce the unused space.
Most installations do not allocate shared partitions, that is the IPL SYS SPSIZE parameter is zero.
If your SPSIZE is not zero and your shared partitions are not yet allocated, you need to reduce the UNUSED space by the SPSIZE value. The resulting unused space may be available for other shared area (24 bit) resources defined during IPL.
There is another option too: If your UNUSED value is close to one MB, you may adapt system sources defind during IPL to reduce the shared area (24 bit) to get to a lower MB boundary, which increases the private area below the 16 MB line. ... but be careful, this change very depends on your system layout, workload and needs some more fine tuning.
Please change the IPL values only, if you need additional resources. Change one parameter at a time and verify the resulting unused space afterwards. Be aware that parameters such as NPARTS may require additional shared space, when partitions are allocated/started.