Recommendation on assigning resources on ESXi 4.0

How would you recommend assigning resources for cpu and memory for the following setup:

- running ESXi 4.0 on HP ML350, 8Gb ram, 2 Xeon 2.33Ghz, 4 x 146SAS 15k
- for now, will run only 1 VM for SBS2008 Standard. Main use: file server, Exchange
- later on (6 months or more): might add a VM for BES server or Terminal Server, maybe both

If I assign all resources and 100% utilization to this single VM, what will be the impact on the SBS2008 OS when I will reduce its resources (ie: assign only 1 cpu instead of 2: will I need to reconfigure the OS) ?


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Requirement for install sbs 2008 is 4GB RAM and 1 CPU. Its good to stick with that to start with.
But it depends on how many users work on the sbs, especially how big will the exchange database be and what other application you install on the sbs.
You can add a cpu later without problems. windows will install the right hall when it boots up. Downgrade to single cpu was a problem with 2003. Don't know if this is still a problem with 2008, because it did not change the HAL back to single cpu.
ndidomenicoAuthor Commented:
The server has now 2 cpu's and 8 Gb. So I should assign 100% of both cpu's the the SBS2008, as well as all 8 Gb of ram ?
It's a fairly small environment: 12 users, Exchange DB of about 15Gb.
Well, first off, you never assign "all" host resources as the host itself uses some of those resources. But, when you create any VM, you assign resources based off the specifications for that particular OS, server OS version, or app. I myself will assign slightly more resources than the recommended amt for growth and unexpected overusage potential. Hope that helps.

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Assign 1 CPU and watch the performance. Maybe add another. Assign 4GB. You can add later if you want, but start with the least possible. So you have resources for other servers in the future.
ndidomenicoAuthor Commented:
So eventhough there are presently 2 cpu's installed, you recommend assigning only 1 cpu to this first VM, if the performance is adequate ? Why not assign the maximum available now (even if it's an overkill for the moment) and later transfer some of the resources to a new 2nd VM ?
I agree with McClane with the CPU resource allocation. For CPU, you can never assign more  vCPUs than the host physically has. So, if your ESX host has 2 CPUs, you cannot add more than 2 vCPUs. For RAM, add the recommended amt for SBS2K8. I would keep some 'spare' RAM to be able to add more VMs, altho I would add more RAM overall if you can...8GB isn't enough, but certainly enough for your 1 VM to start with.

If you assign more CPU than is needed, you can actually hurt performance of the VM (you can read more about why this is in the Resource Mgmt Guide:

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For what? The SBS won't use all the CPUs and you have more work to do later. And it is possible that you have less performance then with just one or 2 cpus. Thats because the scheduler has to schedule all cores you assigned for the vm and all other vm's have to wait till the cores are free again. You can imagine that it harder to free 4 cores then just 1 of more machines are on the host up and running.
 And you should consider that the host also needs some amount of RAM and CPU to do his job.
ndidomenicoAuthor Commented:
So I will use the 8 Gb for this VM. If other VM's come in later, I will then add RAM to the server.
For CPU's, I guess I have to find what is the number of recommended cpu's for my SBS2008 Standard version. Anyone has info or links about the SBS2008 Std recommendations ?
This server has 2 Xeon QuadCore E5520 2.26Ghz processors. Should I count them as 8 processors when checking the recommendations about cpu's for my OS ?  
coolsport00Commented: shouldn't use ALL your RAM. The host needs to use some of it. Here's is the sys req's for SBS2K8:

It says here to use 4GB. I would probably keep it at that or maybe 5GB and keep some left over for your host. Yes, configure only 1 CPU and yes, you would think of your server as having 8 CPUs. Hopet that helps.

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