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The Unisys Clearpath/MCP runs on Xeons, so I don't think there is CPU hot-swapping. I don't know about physically removing a drawer, but on IBM Z, if there is

The Unisys Clearpath/MCP runs on Xeons, so I don't think there is CPU hot-swapping. I don't know about physically removing a drawer, but on IBM Z, if there is a un-recoverable processor error, it will be shut down, and another spare processor brought on-line to take over, transparently. I don't know how licensing/costs ties into the CPU/RAM spares.

skissane 1y ago
> The Unisys Clearpath/MCP runs on Xeons, so I don't think there is CPU hot-swapping. Nowadays it is a software emulator that runs under Linux – so if the Linux kernel and hardware you are running it on supports CPU hot-swap, then the underlying OS will. I believe at one point Unisys would only let you run it on their own branded x86 servers, they now let people run it in Azure, and I'm sure Microsoft isn't using Unisys hardware for that. Running Linux in a VM, the hypervisor can implement hotplug whether or not the underlying server hardware physically does. Of course, without physical CPU hot-swap, it may not add much to reliability, but it still can potentially help with scaling. If you hotplug a new virtual CPU into the Linux VM, you'd probably want to hotplug another emulated mainframe CPU into the mainframe CPU emulator at the same time. No idea if Unisys actually supports that, but they easily could, it is just software – the Linux kernel sends a udev event to userspace when CPUs are plugged/unplugged, and you could use that to propagate the same event into the mainframe emulator.