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only one machine when running VT-x?
Posted: 29. Jan 2009, 22:39
by ToddAndMargo
Hi All,
Base: CentOS 5.2
VM: VBox 2.1.2
I have my XP VM set to use VT-x. My other, I do not.
When I try to run one of the others when XP is running, VBOX refuses, giving me an error messages about only one VT-x at a time.
Is there a way around this? Do I have to turn off my VT-x in XP? (Will that be much slower?)
Many thanks,
-T
Posted: 30. Jan 2009, 13:46
by TerryE
C'mon Todd. Exact error message, please! It's very difficult trying to tracks this sort of thing down. For example, if you want to check the source, most grep tools don't offer an option
--psychic="error messages about only one VT-x at a time" 
Posted: 30. Jan 2009, 19:31
by ToddAndMargo
TerryE wrote:C'mon Todd. Exact error message, please! ... most grep tools don't offer an option
--psychic="error messages about only one VT-x at a time"
Just tested, they all will fire up, if I turn VT-x on. Just one on and one off is giving a problem.
-T
With XP (VB-WinXP) running (VT-x enabled), starting w7 (VB-W7beta) with VT-x disabled gives:
Code: Select all
echo "Start VB-W7beta" | Psychic --dumbdumb forgoterrormessageoption
An active VM already uses Intel VT-x hardware acceleration. It is not allowed to simultaneously use software virtualization.
(VERR_ACCESS_DENIED).
Unknown error creating VM (VERR_ACCESS_DENIED).
Result Code:
NS_ERROR_FAILURE (0x80004005)
Component:
Console
Interface:
IConsole {e3c6d4a1-a935-47ca-b16d-f9e9c496e53e}
Posted: 31. Jan 2009, 00:59
by Sasquatch
That is the whole issue. If you have one VM with VT-x on, all others need to have it enabled. This is in the manual too, you can't have both options (software and hardware virtualisation) at the same time.
Posted: 1. Feb 2009, 16:01
by TerryE
Thanks Tod. As Sasquatch says, a functional limitation of VBox is that the VM monitor (VMM) can only run in one of two modes S/W or H/W assist. It can't run two VMs, one of each, at the same time.
My recommendation is that if you have a recent VT-x enabled CPU then you use H/W enabled for all of your VMs. At worst it runs no slower and in many cases runs a lot better (say the VM overhead is 5% rather than 7%, which in thoughput terms isn't a lot).