DFSMSrmm uses the mounted volume volser by default. The mounted volume volser is taken from the VOL1 label if it is successfully read from the volume. If you have DEVSUPxx VOLNSNS set and the VOL1 label cannot be read, OPEN could have obtained the mounted volume volser from the VOLID mark. In that case and any other case where there is no VOL1 label, DFSMSrmm uses the mounted volume volser provided by OPEN. In order to correctly support duplicate volumes (that are defined to DFSMSrmm) and support OPENRULE with IGNORE, for OPENRULE IGNORE processing only, DFSMSrmm first uses the system managed library vision system volser, then when the mounted volume and requested volume are different DFSMSrmm uses the requested volume volser to check if the volume is defined to DFSMSrmm and that the VOL1 label volser is correctly defined for that volume.

Alternatively, you can customize the EDGUX100 sample exit to use the requested volser, by setting the PL100_SET_IGNORE_REQUESTED bit, as described in EDG_EXIT100 parameter list. The requested volser is obtained either from JCL or from the dynamic allocation request.