Review your data set name block (DSNB) counts to determine if enough DSNBs exist to support a large increase due to data set stacking. The CA Vtape Externalization process stacks Virtual Volumes onto Backstore Tapes. CA 1 consumes one DSNB for each Virtual Volume that is stacked starting with the second Virtual Volume stacked. If 100 Virtual Volumes are stacked on a Backstore Tape, 99 DSNBs will be consumed.
DSNBs exist for the life of the Backstore Tape, not the life of the Virtual Volume. As long as one of the Virtual Volumes on a Backstore Tape containing 100 Virtual Volumes remains unexpired, all 99 DSNBs are maintained, including the expired ones. As CA Vtape usage increases over time, more DSNBs will be used and maintained for expired Virtual Volumes. If all DSNBs are consumed, tape processing stops until the Tape Management Catalog (TMC) is increased in size and the number of DSNBs is increased.
Running the RECYCLE utility to recover fragmented Backstore Tape space will also recover expired DSNBs. However, a large increase in the number of DSNBs will still occur. A good rule is to have three DSNBs available for each Virtual Volume defined. If 50,000 Virtual Volumes were defined to CA 1, 150,000 free DSNBs should be made available.
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