WAIT | NOWAIT are mutually exclusive, optional parameters used to specify whether you want to wait for the HBACKDS command to complete.

WAIT specifies that you want to wait for the HBACKDS command to complete. When DFSMShsm successfully completes the HBACKDS process, the ARC1000I message is issued. If the HBACKDS process does not complete successfully, the ARC1001I message is issued. If you press the TSO Attention key before DFSMShsm completes the command, DFSMShsm issues the ARC1800I message and does not issue the ARC1000I message.

NOWAIT specifies that you do not want to wait for the HBACKDS command to complete. When DFSMShsm successfully receives the request, the ARC1007I message is issued. After DFSMShsm successfully completes the HBACKDS command, the ARC1000I message is issued. If the HBACKDS command does not complete successfully, the ARC1001I message is issued.