In Hyper-V (and Virtual Server) we allow you to configure a CPU resource reservation, limit and relative weight. This is usually used for providing performance guarantees for virtual machines – however – last weekend I found a rather obscure usage for this set of settings.
Last weekend there were a number of tests that I needed to run on the RC release of Hyper-V as we were preparing for the formal release. In order to do this I just grabbed one of my old (slightly dodgy) computers. After installing Windows Server 2008, and the RC build of Hyper-V, I started setting up a number of virtual machines.
When I was ~80% through guest OS installation the computer spontaneously powered off.
When I turned it back on the BIOS came up and told me that the system had powered off because I had exceeded thermal limits on the hardware! After starting up the system again and resuming OS installation I ran for about 5 minutes before the system powered off again due to exceeding thermal limits.
At this stage it was apparent that my hardware was busted, but I really did not want to have to rebuild on a new system. So in a moment of inspiration I bought the system up and went through each virtual machine and set the processor limit to 50%. Once I did this I was able to complete my testing without overheating the computer.
Two hours later – my testing was completed – and a post-it note was put on the physical computer to remind me not to use this computer in the future.