We have a VM that currently is setup for one cpu when go to edit its settings in the VCenter Server but the physical machine actually has 2 quad core processors in it. Can we change those settings when the power is off to lets say 2 dual core processors on that VM or would you have to reload the whole thing as far as the guest os to make that kind of a change.
Just shutdown the VM then edit the settings and increase the vCPU amount to 2 or 4 and then power the VM back on. The changes should be picked up automaticaly by the VM upon power on.
people get tired of hearing this, but the answer is it depends. If your quest is Windows, then depending on the version you may or may not have to change the HAL. If it is Linux you will have to boot to the SMP kernel.
Now, let's delve into the setup and the the whys. First, you say you have 2 quad core processors and want to give the VM two dual core processors. What ESX will tell you is you have 8 processors, as each core is counted as a processor. So you would have to give your guest 4 processors. Now for the why? Only a very heavily utilized guest will use 4 virtual processors. I'd only do this with a large SQL or Orcale database, and even then I'd have a long talk with the DBA about why this is required. Most apps aren't multi-threaded and what you will end up with is one CPU doing all the work and the other just sitting there twiddling it's virtual thumbs. Remember you want as many guests as possible consolidated on one host, so try very hard not to over spec your guests. Vendors have conditioned administrators to buy 2 processor quad core running at minimum 3 GHZ when in reality their app would run on a P II. But that's been the trend for troubleshooting over the past years. First reboot, if that doesn't work throw more RAM at it, if that doesn't work throw another CPU at it, if that doesn't work, then we will investigate the issue.
Also be aware that the O/S in the VM needs to be able to take advantage of the multiple processors - if it is not the O/S does not support multiple processors you will run the risk of seriously impairing the performance of the VM - Also do you have reasons why you want to add an additinal virtual CPU to the VM?If you are doing it just because you can you will also be heading down a path that could affect the performance of your VM - the vmkernel schedules the virtual CPUs simultaneously which means if the vmkernel can not schedule all virtual CPUs none will get scheduled affecting vm performance
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It is a WIndows 20003 R2 Guest OS and the main application on that machine is SQL Server 2000 Standard Edition. So I would like SQL Server to be able to take advantage of at least 2 processors.