In your virtualbox, choose IO APIC, otherwise your windows will not be happy when booting as I assume it has previously started with IO APIC
Your solution in this topic addresses this issue by having two system boot profiles one with and one without APIC.
I am uncomfortable adding normal users to the group disk. You are now able with a little bit of finger trouble such as ls -l > /dev/sda to trash your system. I think that the idea of having a service account (which is in the disk group) to run VBox in, configuring sudoers, and some wrapper scripts which set VBOX_USER_HOME and start VBox in this account is far safer. I need to write these, but I haven't set this up yet as I rarely use raw partitions. At the moment when I do, I think on balance it is safer to do so using the same trick and sudoing into root to do the VBox command, and sudo chowning the files back to my ownership on exit.
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I'm sure if this applies or not fromt he troubleshooting section of the guide:
11.3. Linux guests
11.3.1. Linux guests may cause a high CPU load
Some Linux guests may cause a high CPU load even if the guest system appears to be idle. This can be caused by a high timer frequency of the guest kernel. Some Linux distributions, for example Fedora, ship a Linux kernel configured for a timer frequency of 1000Hz. We recommend to recompile the guest kernel and to select a timer frequency of 100Hz.
You are right on both items - I was adding the raw disk management topic because it is true that my answer is irrelevant in case of virtual disks as, of course, Windows will detect and use a a single CPU HAL and _this_ version of high CPU problem will not happen. DO you think we should make a more complete well-described guide ?