DFSMSrmm validates WORM tapes at OPEN time and rejects any WORM tapes using this criteria.

• DFSMSrmm ensures that the mounted volume has the correct WWID. DFSMSrmm obtains the WWID for a WORM tape from the tape drive when the volume is mounted and used or when you define the WORM tape to DFSMSrmm using the RMM TSO subcommands.
• When DFSMSrmm has a Write Mount Count for a WORM media, DFSMSrmm ensures that the mounted volume write mount count matches the value recorded in the DFSMSrmm control database.
• DFSMSrmm enforces the MASTEROVERWRITE(ADD) option on a WORM tape that is in master status. This is done to ensure that you see a message from DFSMSrmm rather than one of a number of symptoms as a result of the tape drive preventing overwrites. When a WORM volume is in user status, DFSMSrmm does not enforce the same checks, but does prevent any updates to information records in the DFSMSrmm control data set for existing data sets that are written to the volume. In the latter case, any write or rewrite of data on the volume is subject to the checks built into IBM's WORM tape functionality, so it may or may not be allowed.

For a WORM tape that has been successfully validated, DFSMSrmm records the WWID and write mount count from the tape drive if there are no values defined to DFSMSrmm.