Depending on the environment, SMS invokes some or all of the ACS routines in the following order:

1. Data class
2. Storage class
3. Management class
4. Storage group

DFSMSrmm supports the SMS pre-ACS interface. The SMS subsystem calls DFSMSrmm before the data class ACS routine obtains control. Then, DFSMSrmm optionally sets the initial value for the ACS routine MSPOOL and MSPOLICY read-only variables if the pre-ACS installation exit has not done so. However, DFSMSrmm does not use the installation exit.

See z/OS DFSMSrmm Implementation and Customization Guide for detailed information on the DFSMSrmm support for the SMS pre-ACS interface. Or, check with your tape management vendors for information on support for the variables.

When UNIT=AFF is specified on the JCL DD statement and the ACS routine determines that the AFF'ed and AFF'ing DDs use different SMS constructs, an unexpected SMS construct might be used.