Resizing a Windows Server guest

[MariusRoma]

I need to implement a Windiws Server 2008 R2 guest VM acting as a Remote Desktop Server.

At the moment I can't predict how much the VM will be used, including the number of users and the way they will use the VM.

I am considering creating a Windows VM with an arbitrary number of vCPU (let's say 2) and an arbitrary amount of vRAM (let's say, 8 GB).

I know that if I see that the VM gets overloaded (using Microsoft Performance Monitor) I can add more vCPUs and increase vRAM size.

Is there any guideline to change the resources assigned to a VM?

I mean, given that Windows allows adding CPUs and RAM, is it advisable to start with a minimal configuration and to increase it or to start with a larger configuration and recduce it?

Regards

marius

[Troy_Clavell]

it's always best to provide your guest with the resources it needs to function optimally.  vCPU and vRAM are two performance metrics which are pretty easy to identify if there is a bottleneck.  Also, with the ability to hot add, you can adjust the resources dynamically.  We typically start all our 2k8r2 guests with 2vCPU/4GBvRAM

[jdptechnc]

I have a minimum standard of 1 vCPU / 4GB RAM / 60GB disk for my Windows 2008 VMs, but if I think the application will call for more resources, I'll add a vCPU and some memory.  I also tend to look at the vendor's hardware recommendations; In particular Microsoft has been doing a decent job lately of laying these out for their roles and different server apps because they have a vested interest in virtualization these days as well.  So it would be beneficial to see what Technet has to say on recommendations for the number of users and the roles you need to implement, in addition to the software vendor for the client apps that will be run on the Terminal Server.  If very many concurrent users are going to be using the server, 2 vCPU/8GB could be a bit low.

The other end of the spectrum is when people request 4 or 8 CPUs and 32GB RAM, "just in case they need it".  If I can determine that is the case, they get what they get (much less resources) and I'll add more later if the situation warrants it.

[mattandes]

It can be hard to determine where to start out at especially when you don't have any hard requirements but from my experience if you over allocate resources to a VM and it doesn't need it, you'll have an uphill battle scaling the VM back down. Also, another concern you have to worry about is that if you over commit resources is that you can cause issues for yourself later on down the road as far as CPU issues (This post describes a little bit about what I'm talking about. http://communities.vmware.com/message/2249707#2249707) and possible memory contention issues. As a general rule of thumb you want to start out small and grow as needed especially when user requesting the VM has no idea what kind of resource utilization they're going to have.

As for what we use in the environment I manage, our Server 2008 R2 template only has 1 vCPU and 2 GB of RAM to start out with and we scale it up as needed based off the requirements but if the user doesn't know what it needs or doesn't ask for a certain amount they usually get the base template amount. Keep in mind part that part of the reason our resources are set were they are is because we normally don't have a lot of users hitting any of our servers so they don't usually require a ton of resources.