In-Service Migration from iSeries to rSeries Using a Mixed-Platform HA Pair

I do not have a technical issue with mixed platform redundancy pairing. I have procedural and organizational issues with using mixed platforms.

I have experienced issues with multiple migrations to new hardware. The issues have caused a return to using the older hardware. Being able to revert back to older hardware quickly and without issue can be more important that implementing the new hardware.    

It's quicker to revert back to an older pair of devices. Then removing new devices and adding back old devices to a redundant pair.

In some organizations it not possible to discover all the dependencies before moving traffic to new hardware.  The dependencies are are found after moving to the new hardware because an application stopped working. The only way to recover the application is restoring the older hardware.