The TAPESPANSIZE optional parameter of the SETSYS command can be used to reduce the occurrences of data sets spanning tape volumes. This is of benefit when running certain functions such as recall, recover, and recycle. When a data set spans tape volumes, a recall or recovery of that data set requires two tape mounts rather than one.
If you are recycling a connected set of tape volumes, recycle processing determines whether the average of all the tapes in the connected set meets the selection criteria and optionally whether the first volume in the connected set also meets the selection criteria. If not, no tapes in the connected set are recycled, potentially leaving some tapes with very little data on them. You can modify your installation's use of recycling for connected sets through the CHECKFIRST parameter.
With the SETSYS TAPESPANSIZE command, you can specify a value between 0 and 4000. This value represents the maximum number of megabytes of tape that DFSMShsm can leave unused while trying to eliminate spanning data sets. To state this differently, this value is the minimum size of a data set that is allowed to span tape volumes. Data sets whose size is less than the value do not normally span volumes. Only those data sets whose size is greater than or equal to the specified value are allowed to span volumes. The data written to tape results from compression by the tape subsystem, so predictions of that resultant size are not always correct. Therefore, spanning can occur for some data sets that do not compress as expected.