Considerations when changing Storage Management Subsystem configurations

When activating a new SMS configuration, you have two options for keeping the currently active SMS configuration information:

Keep, but never modify, the original SCDS from which the current SMS configuration was activated.
If you choose this method, you need to maintain a log of all status changes, such as VARY storage group commands, that you make to the currently active SMS configuration. If in the future you activate a different SMS configuration but then decide you want to fall back to your original, you can reactivate the SCDS. You lose all the status changes you have made since activating the SCDS and must reenter them, but you return to the original SMS configuration.
Save the current active SMS configuration using the SETSMS operator command:
```
SETSMS SAVEACDS(ACDS.FALLBACK)
```
This is the recommended alternative for keeping the SMS configuration information.
ACDS.FALLBACK must be an existing, already allocated data set. By using this command, you not only save the current storage management policy in ACDS.FALLBACK, but you also save the status changes you have made since the original SCDS was activated. You can then activate the new SMS configuration. If in the future you decide you want to fall back to the original SMS configuration, you can use the SETSMS operator command to reactivate it:
```
SETSMS ACDS(ACDS.FALLBACK)
```
This alternative is useful if you have altered the SCDS that you originally activated.

Restriction: Any SMS status that is changed using the SETSMS command is overridden by the MVS status if a new configuration is activated. See z/OS MVS System Commands for information on the SETSMS operator command.

Requirement: All systems in the SMS complex must be running in the same mode.

When an SMS control data set that supports only eight names is accessed for update on a system running in 32-name mode, you must convert the data set to a new, incompatible format in order to support 32 names. Confirm this conversion using the operator console or the ISMF. This conversion is permanent, so you should make copies of your control data sets before the system mode is converted.