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Testing OS Simulation EXECs Using CMS Sparse Files

You might want to test your OS simulation EXECs to make sure that they can write across multiple tapes. You can do so by creating large sparse files and writing them to tape. Sparse files are large, but occupy little actual disk space. Create them shown as follows:

/* This exec creates a large file */
address ‘COMMAND'
‘ERASE LARGE FILE A'
‘EXECIO 1 DISKW LARGE FILE A 1000000 F 80 ( FINIS STRING End'
exit RC

The file created contains one million records, but easily fits on even the smallest CMS disk. By simply altering the number of records in the sparse file, you can change the number of tapes required to hold it.

If, during testing, you want to read a tape created using sparse files but do not have enough disk space, change your output FILEDEF command to:

filedef  ddname  dummy

This command discards all the information read from the tape while allowing the reading of the tape to continue. This allows you to see, during testing, that each tape was mounted and read, without actually creating the file on disk. Once your testing is complete, you can change the FILEDEF command to specify the proper value.