You can't remove DSNBs that have been used with the TMSXTEND utility program.
If you need to do this, you will have to use TMSSPLIT to export all of the tape volumes and associated DSNBs, format a new TMC with the reduced amount of DSNBs, and then run TMSMERGE to rebuild the entries.
The below procedure has been updated as well for those sites using an Extended Format TMC.
Internal Split/Merge Procedure for an Extended Format TMC
In the event the DSNB allocation contains a disproportionately high number of unused DSNBs, and there is no anticipation of future growth, it is possible to reduce the allocation by performing a split/merge operation.
The following process must be executed in an environment with no tape processing occuring, and no CA 1 batch or online processing being performed:
Note: For information, see the Administration Guide.
The TMSBLDVR SYSIN control statements must specify all volume ranges in the production TMC, and the desired reduced number of DSNB records you wish to allocate.
i) Specify ‘PARM=NEW’
When this parameter is specified, a new TMC is formatted without copying volume ranges or DSNB records from an input TMC. The new TMC must be preallocated and cataloged. CA 1 does not have to be active or batch active to run with PARM=NEW.
ii) The ‘//TMCNEW DD’ specifies a preallocated new TMC data set.
This DD statement is required if PARM=NEW is specified. A newly allocated, empty TMC should be specified.