This is another very common way to share an ATL or VTS when the Tape Library is not actually partitioned. This is almost the same as having the Tape Library partitioned, but provides the user with more flexibility in terms of adjusting the size (number of volumes or number of devices) on each side without having to redefine the partitions. For basic operation, the CA 1® Tape Management supplied entry and eject exits do not require modifications. However, if foreign tapes are inserted into the ATL and used on one of the systems, a more complicated version of the entry exit is needed.
For an example, we assume that CPUA and CPUB share a Tape Library with separate TMCs and TCDBs, and we want to allow foreign tapes to be used as input on CPUA. In this case, the entry and eject exits for CPUB remain unchanged. CPUA cartridges are considered foreign to CPUB, when CPUB is notified that a CPUA cartridge is inserted. The CPUA cartridge is ignored. When CPUA is notified it assigns the correct status (SCRATCH or PRIVATE) and takes ownership of the cartridge.
However, in the same example the entry exit on CPUA needs to be modified and is more complicated. In the CA 1–supplied entry exit (CTSUXENT in the hlq.CTAPSAMP library), a code needs to be added at label RC16. This can be done using the usermod CTSJUCBX.
If the volume inserted is defined to CPUB (which means a table needs to be created or a set of compares needs to be done to see if the volser matches those defined to CPUB,) then the instruction LA R15,UXEIGNOR needs to be performed (followed by the branch to EXIT). However, if the tape is not defined to CPUB (again, based on the volser) branch to label RC8 (which puts the foreign tape into PRIVATE status and take ownership of it on CPUA.) Depending upon the volser standards on CPUB, this can be very simple (look for a cartridge starting with B0 or B1) or very complicated.
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