How to add more RAM and CPU's to a VMware sserver?


It has been suggested to add more RAM to a Virtual Server.  In the near future I may need to add more CPU's as well.  The existing specs are shown below:

My question is how may I properly add more RAM and CPU's to a Virtual Server (Windows 2008 R2 Sp1).  This is an important server in our environment and I want to make sure that I will be doing that correctly?  Yes we do have backups (VEEAM Backup and Replication) and I plan to wait to do any changes until tonight's backup (after hours) has completed.

In the past I have simply powered-off the VM and then added the amount of RAM to the virtual Server and then powered the virtual machine back on.  Please see my specific questions below:

1.  Is the correct way to add/remove RAM to a Virtual Server to:
         a.  Power-off the VM
         b.  Then added the amount of RAM to the virtual Server
         c.  Then powered the virtual machine back on.
         d.  Check for VM functionality.

2.  If I need to add more CPU's, is it the same process?
         a.  The Vendor just recommended that I change the Virtual Sockets = 2.
                  i. And to change cores per socket to 4.
         b.  is changing the CPU's the same process as changing the RAM?

3.  Whenever I have added CPU's in the past, I always have powered off the VM and made changes; but, you see a warning message stating that changing the CPU's may make the Operating system less stable.  See the screen shot above.
         a.  Is this a general message that comes up?
         b.  II have never had that problem yet.
         c.   Is it not advisable to change CPU's on a VM that has already been in production?
         d.  I have done it before and it ahs worked for the better on other servers.
PkafkasNetwork EngineerAsked:
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The process seems right to me. Power off the VM and add the RAM. Same with CPU. I've never had any issues changing CPU for a VM in production but having backups before making any changes is important in any case.
I should add that it's probably not a good idea to go from multi cpu to single gpu but this isn't what you seem to be wanting to do anyway.
Andrew Hancock (VMware vExpert / EE MVE^2)VMware and Virtualization ConsultantCommented:
1. Correct

2. I would always recommend, add sockets, not cores, unless you have a specific license requirement e.g. license by cores. So if your vendor states you need 4 processors in your server, select 4 sockets.

3. It always occurs, this is just a warning message, older operating systems did not support plug and play, and require a switch of software HAL.

You may want to enable Hot Plug CPU and Hot Plug Memory, if your OS Support supports these functions, and you have the correct vSphere Licenses.

Also, have a read of this....

vSMP (virtual SMP) can affect virtual machine performance, when adding too many vCPUs to virtual machines that cannot use the vCPUs effectly, e.g. Servers than can use vSMP correctly :- SQL Server, Exchange Server.

This is true, many VMware Administrators, think adding lots of processors, will increase performance - wrong! (and because they can, they just go silly!). Sometimes there is confusion between cores and processors. But what we are adding is additional processors in the virtual machine.

So 4 vCPU, to the VM is a 4 Way SMP (Quad Processor Server), if you have Enterprise Plus license you can add 8, (and only if you have the correct OS License will the OS recognise them all).

If applications, can take advantage e.g. Exchange, SQL, adding additional processors, can/may increase performance.

So usual rule of thumb is try 1 vCPU, then try 2 vCPU, knock back to 1 vCPU if performance is affected. and only use vSMP if the VM can take advantage.

Example, VM with 4 vCPUs allocated!

My simple laymans explaination of the "scheduler!"

As you have assigned 4 vCPUs, to this VM, the VMware scheulder, has to wait until 4 cores are free and available, to do this, it has to pause the first cores, until the 4th is available, during this timeframe, the paused cores are not available for processes, this is my simplistic view, but bottom line is adding more vCPUs to a VM, may not give you the performance benefits you think, unless the VM, it's applications are optimised for additional vCPUs.

See here

see here

also there is a document here about the CPU scheduler

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Bryant SchaperCommented:
I second the caution about a lot of vCPUs.  I had a client with many 8+ servers and the environment was slow.  Admins build systems like they were physical.  Reduced to 1 and 2 vCPUs and improved performance a bunch.
PkafkasNetwork EngineerAuthor Commented:
OK, I believe the core question of how to properly change the number of RAM and CPU's has been answered.  I have another question regarding how to configure 8 CPU's from 4 which I will create a new question for.

Another contact stated the following:

"Based on the information I gave you and a couple of discussions I have had with a VMware vExpert I know, if the vendor believes the vCPU count needs to be 8 then change the socket count to 8 and leave the core count at 1. But I would again stress the need to perform the NUMA check outlined in that article ( ) so you don't bring the vCPU count up to a point where you cross the NUMA boundary.

First off you have to look at the NUMA boundaries of the host to make sure we don't increase the number of vCPUs to a point where it causes processing to cross this boundary.   You could check if you are familiar with PuTTY. "
Mohammed KhawajaManager - Infrastructure:  Information TechnologyCommented:
I agree with Andrew.  I would second hot-add feature where CPU and RAM can be added while the OS is powered on and running.
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