Data sets migrated to tape are written as standard labeled tape files; there are multiple files per tape. The first data set written does CA Disk create the dummy file it is standard label file 1 (1,SL). The first data set migrated is standard label file 2 (2,SL). The file number is incremented by one for each data set on the tape. If CA Disk predicts that the next data set will not fit on the current tape, it causes a new tape to be mounted and begins again with file 1.
If a data set is too large to fit on one tape (or if CA Disk thought the next data set would fit but it doesn't because the tape is shorter than expected), CA Disk will continue writing the data set on additional tapes as needed. When processing for that data set is complete, CA Disk will ask for a new tape to be mounted for subsequent data sets and will reset the file number to 1.
CA Disk does not stack additional data sets with incremented file numbers on the end of multivolume tapes. The reason is, for the operating system to correctly locate those file numbers for subsequent jobs that need the data sets; each tape in the multivolume set must be mounted, spun to the end to find and count the file numbers, and rewound, until the correct tape and file number are found. By not allowing this, CA Disk ensures that every data set needed can be found on the first tape that is mounted.
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