Adding CPU

[max2001]

Let us assume that we have an ESX Box with 2 CPUs (Quad

core).

1^st question: does that equal to 8 Virtual CPUs?

2^nd question: when you attempt to add another CPU

for a gust OS, Virtual Centers displays a message: “changing the number of

virtual processors after the guest OS is installed may make your virtual

machine unstable”

Why would that make the VM unstable as long as the OS is SMP

aware and that Virtual SMP is by default enabled in ESX?

Thanks.

[admin]

Let us assume that we have an ESX Box with 2 CPUs (Quad

core).

1^st question: does that equal to 8 Virtual CPUs?

Yes.

You can confirm this through the VI Client by clicking on the host -> "Configuration" tab -> Processors

or through the command line by typing the command esxtop

2^nd question: when you attempt to add another CPU

for a gust OS, Virtual Centers displays a message: “changing the number of

virtual processors after the guest OS is installed may make your virtual

machine unstable”

Why would that make the VM unstable as long as the OS is SMP

aware and that Virtual SMP is by default enabled in ESX?

That warning message is there because some guest operating systems cannot handle the addition of another CPU unless they have been configured for multiprocessor support.

This is the same in both physical and virtual environments.

If the guest operating system has already been configured for SMP/multiprocessor by the installation of the appropriate kernel/HAL, you can safely ignore the warning message and add the CPU without fear of instability.

[weinstein5]

1) It equals 8 LCPUs (Logical CPUs) which are treated as PCPUs (Physical CPUs) so not VCPUS (Virtual CPUs) - this term for CPUs assigned to a VM

2) You are correct as long as the O/S is SMP aware it should not be able a problem - that warning is to remind administrators there are O/Ses that require a change in HAL or kernel to support multiprocessing -