Description: Before z/OS V1R13, the flag at MCVT+C8 X'80' was used to prevent the SMS MVT chain rebuild at the beginning of primary space management and at the beginning of interval migration, based on the current SMS storage group definitions. If the SMS storage groups had not been changed and no new SMS volumes had been added since the last time primary space management or interval migration was run, you could prevent the SMS MVT chain from being needlessly rebuilt or refreshed by entering the following PATCH command:
PATCH .MCVT.+C8 BITS(1.......)
Starting with z/OS V1R13, this flag is maintained automatically by DFSMShsm. DFSMShsm checks for the occurrence of an ENF 15 event at the beginning of primary space management, at the beginning of interval migration, and at the beginning of on-demand migration. When an ENF 15 event is reported, DFSMShsm performs an SMS MVT chain rebuild or refresh. After a successful SMS MVT chain rebuild, DFSMShsm does not rebuild or refresh the MVT chain until the next SMS configuration change (that is, the next ENF 15 event).
Starting with z/OS V1R13, DFSMShsm does not take into account the PATCH .MCVT.+C8 BITS(1.......) command. Nevertheless, it is recommended to remove this patch command from the ARCCMDxx parmlib member of SYS1.PARMLIB to avoid any misunderstanding.
| Element or feature: | DFSMShsm. |
| When change was introduced: | z/OS V1R13. |
| Applies to migration from: | z/OS V1R12. |
| Timing: | Before the first IPL of z/OS V2R1. |
| Is the migration action required? | No, but recommended because starting from z/OS V1R13, the patch command no longer performs a useful function other than what is already handled automatically by DFSMShsm. Additionally, it been discovered in the past that leaving unnecessary useless patches in DFSMShsm's startup procedures can cause confusion and potential problems. |
| Target system hardware requirements: | None. |
| Target system software requirements: | None. |
| Other system (coexistence or fallback) requirements: | Remove this patch when all systems are at z/OS V2R1 if a common DFSMShsm's startup procedure is shared with downlevel systems. |
| Restrictions: | None. |
| System impacts: | None. |
| Related IBM Health Checker for z/OS check: | None. |
Steps to take: Remove PATCH .MCVT.+C8 BITS(1.......) from the ARCCMDxx parmlib member of SYS1.PARMLIB.
Reference information: None.