This is all true, but you still can't rely on increased hardware quality if you can't afford any downtime due to moving (a one-time event) a server.
Also, that doesn't cover other problems mentioned here, like natural disasters, ISP problems, etc.
Also, that doesn't cover other problems mentioned here, like natural disasters, ISP problems, etc.
Also cost does come in play as well. Multiple physical links in would be very expensive for what sounds like internal services. Likewise a natural disaster might cause bigger issues to the company than those internal services going down. They might still have offsite back ups (I'd hope they would!) so at least they can recover the services but the cost of having a live redundancy system off site might not justify those risk factors.
The customers requires are definitely unreasonable though. I'd hope those systems are regularly patched, in which case when is downtime for that scheduled and why is that acceptable but not when you're physically moving the server? I doesn't really make much sense; but then "not making much sense" also quite a common problem when providing IT services for others.
In general, we don't know much about this case. It's a post on Reddit, might not even be true. As is, it doesn't make much sense, but we don't know all the details, so maybe we jumped to conclusions.
Mainframe is not just a server. You can hot plug RAM on these things.