When a Virtual Volume is dismounted, it is queued to a stacking group that is processed by the Backstore Engine. The stacking group chosen is the one assigned by the filter that caused CA Vtape to intercept the tape mount request.
If an application data set goes to multiple volumes, the previous Virtual Volume will be queued for Externalization while the next Virtual Volume is being written. This allows the Backstore Engine to Externalize large data sets more quickly to keep the percentage of reusable space in the DASD buffer as high as possible.
After the Virtual Volume is Externalized, it is placed on a queue so its DASD space can be reused when needed to support a new virtual mount request.
The tapes written to by the Backstore Engine during Externalization are collectively referred to as the Backstore Tapes. These tapes can be any mainframe virtual or physical tapes, but not CA Vtape tapes. In other words, CA Vtape will not Externalize its Virtual Volumes to itself.
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