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Hello,

Is it better to run SBS 2011 (essentially Server 2008 R2 w/ Exchange 2010) with 1 virtual processor or 2?

When I setup this VM I had a single quad core Xeon processor and assigned 2 virtual processors to the VM. Now I have 2 quads for a total of 8 cores. A number of months ago I attempted to up the virtual processors to 4 and experience TERRIBLE performance. I then tried 3. Still sucked. Then I went back to 2 and have been here ever since.

I have read that some guest operating systems run better on only 1 virtual processor. Can anyone confirm if SBS 2011 is one of these operating systems?

If so, can anyone point me to instructions on how to convert this OS from 2 to 1 proc? I understand I have to do something w/ the HAL but this sounds scarry.

Any input is much appreciated. Thank you!

1 processor works fine for me. All you should need to do is change the count from 2 to 1 in the guest settings. Just don't turn off io-apic or you will have issues.

Thanks again Perryg,

Do you run SBS 2011 or Server 2008 R2? If so, have you compared performance with 1 vs 2 virtual processors?

Is it the changing of io-apic that requires the changing of the HAL? I have read that some believe io-apic slows down their VM. Of course I can't find those posts at the moment. I just wasted about an hour looking for them. However I just read that it is required for 64-bit OSs.

http://www.virtualbox.org/manual/ch03.h ... 4bitguests

Did I read that right? So with SBS 2011 (Server 2008 R2) which is only available in 64-bit, I absolutely MUST leave it enabled, correct?

Do I only change the virtual processor count when attempting this? Should I disable VT-x? What about PAE/NX or Nested Paging?

I'll do a back up, of course, but should I expect the VM to boot up w/o any new, peculiar issues after this change?

Any good, easy ways to benchmark VM performance before and after changes like this?

Thanks so much for the help!

It's really simple. Just set the processor count to 1 and don't change anything else or you will have issues.
Performance is close to the same although boot time may seem longer. Once booted it should be fine. As for benchmarks look at it this way. If it keeps giving problems with two processors and does not with one this offsets the performance if it stays working. Don't try to use benchmark tools either. They are not designed to work in a virtual environment and give wrong readings.

Well, I tried simply changing from 2 processors to 1 and the VM crashes during startup. I tried 3 times and always the same result. Any ideas why this would be happening?

Thanks.

VBox.log wrote: 00:02:57.083 !!R0-Assertion Failed!!
00:02:57.083 Expression: RT_SUCCESS_NP(rc)
00:02:57.083 Location : D:\tinderbox\win-4.1\src\VBox\VMM\VMMAll\PGMAllPool.cpp(2476) pgmPoolMonitorInsert
00:02:57.083 PGMHandlerPhysicalRegisterEx 0000000293a94000 failed with -1701
00:02:57.083 !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
00:02:57.083 !!
00:02:57.083 !! Guru Meditation -2701 (VERR_VMM_RING0_ASSERTION)
00:02:57.083 !!
00:02:57.083 !!R0-Assertion Failed!!

I would suggest an experiment: allocate much less memory to the VM and lets see how it goes. I would suggest 8192MB (8GB) max. Not one byte more than that.

Hello,

Sorry for the delay. I have been busy and haven't been able to get back to this until now.

8gb of RAM seemed to allow the VM to boot with only 1 proc. But why?

I lowered my ram to 8gb but continued to run 2 procs for a couple weeks to see how it would go. Performance was terrible. I'd really like to be able to allocate more RAM.

What exactly do those errors mean? Why can I allocate more RAM when using 2 procs but not when I use only 1?

Thank you,
Mike