vCPU allocation to a VM

[jkrishna]

Hi,

Could anybody please clarify ,why we can only allocate powers of 2 (1,2,4) as number of processors to a virtual machine , why can't we allocate 3 virtual Processors to a VM.

Please excuse me if this not the correct question.

Regards

Jayakrishna.K

[Chris_S_UK]

Just like in the physical world, the BIOS of the VM isn't designed to work with an odd number of CPUs.

[jkrishna]

Hi,

Could u plz give me any doc, which explains why it is not supported in physical word.

Regards

Jayakrishna.K

[simmetje]

Hi, we accidentally received an IBM x3850 with three Xeon 7140N CPU's. the dealer forgot to order one CPU. We installed ESX3.01 and it's working perfectly.

I'm not sure if Windows would recognize all three CPU's but ESX works fine. In this case an odd number of CPU's seems to be no problem....

Rob.

[jkrishna]

Hi ,

So , what can we conclude , there are machines with 3 Physical CPUs in market??

Regards

Jayakrishna.K

[RParker]

You can't do this in the real world either.

Digital IS binary. That's the reason. 3 CPU would not make sense, since you can't emulate this in a real world situation (unless a physical processor fails). you buy a processor or add a second processor and they would be identical, you can't even boot a machine without a matching pair of pretty much anything, memory, cpu, it's a binary system.

[RParker]

No, I can't validate his claim, but I believe this is not a "real" situation. Maybe it's true, but in my most cases a board can't boot with only 1 memory in the slot, it needs 2. 2 CPU and if it has 4 sockets, it is expecting ALL 4 sockets to be populated.

Even if it did work, I doubt very seriously he has 3 CPU in his configuration, it probably shows 2 only and make the last one invalid, since it realisitcally is.

Besides, why are you trying to force 3 cPU anyway? If you need more CPU just add 4, why try to rewrite the program?

[RParker]

read this web site or take a A++ class, that will give you the information you need.

[simmetje]

Sorry guys, but it's really working with 3 CPU's. Currently hosting 24 VM's in a production cluster that hosts devellopers.

VC shows 3 CPU's working and 12 logical CPU's. (dual core and hyperthreading on).

Like I said, I did not try it with Windows but ESX3 run's fine.

NExt week we will add the 4th CPU that has arrived yesterday so I will try to make a screenshot this week.

Rob.

[virtualdud3]

Well, 3 CPUs, each with 2 cores and hyperthreading enabled equals 6 CPUs cores/12 hardware contexts of execution.

The point being, "6" and "12" are both even numbers.

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[gorto]

This is such an intriguing story - I'm aghast!

My (basic) understanding is that a machine shouldn't get past POST with an odd number of sockets populated or at least the odd socket disabled.

I await the outcome .......

[virtualdud3]

Yeah, even with an even number of CPU cores I'm still not convinced that the 3 CPU machine booting is kosher.

We'll wait and see.

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