Initial tape selection is the activity of selecting the first tape for a tape processing function and is always associated with a tape device type. Tapes and devices are selected and allocated differently in an SMS-managed tape library environment than in a non-SMS-managed, nonlibrary environment.

DFSMShsm selects tapes in the following order:

1. Partial (only if eligible and available). If you are selecting a migration tape, DFSMShsm begins by considering the tape last used by the task. If it is not acceptable, then it selects the eligible partial tape with the highest percentage of written data.
2. Empty
3. Scratch

In a nonlibrary environment, DFSMShsm selects a tape that is compatible with the unit type restriction for the function.

In an SMS-managed tape library, MVS™ allocates a device according to the data class, storage class, and storage group associated with the data set. DFSMShsm, using the above selection order, selects a tape that is compatible with that device.

Partial tapes selected in a duplex environment must have a duplex alternate. (A nonduplexed alternate is an alternate created by user-initiated TAPECOPY.) Empty or scratch tapes selected in a duplex environment will have a scratch tape for the alternate.