Can I use the same FICON link to access both my ESCON devices and my Bus/Tag devices?
It depends largely on how each Bus/Tag device is used today from an operational perspective.
If the Bus/Tag device is dedicated to a single LPAR currently, then the same FICON link can be used to access ESCON devices and Bus/Tag devices. As an example, consider an ESCON tape drive that is accessed by 4 LPARs and a Bus/Tag printer that is accessed by only 1 of the 4 LPARs used by the tape drive. This scenario could be supported on a single FICON link. The CHPID would be defined to have all 4 LPARs in the Access List. The IODEVICE statement for the Bus/Tag device would have a Device Candidate List parameter that would name the single LPAR that can access the Bus/Tag device.
If the Bus/Tag device is currently using a reconfigurable CVC CHPID and needs to be periodically switched from one LPAR to another, then a dedicated FICON link should be allocated for this Bus/Tag device in the Prizm environment. Why? In order to drop the Logical Path connection to device, the CHPID must be configured off to the LPAR. This will affect all other devices on the LPAR using that CHPID, i.e. the ESCON tape drive. Once the Logical Path is dropped, the CHPID can be configured ON to the receiving LPAR. With multi path devices such as tape, it is possible to remove one path to the multi path device in order to move the single path device to a different LPAR, without losing all paths to the device. Once the Single Path device has moved, the CHPID that was configured off can be configured back on.
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