Resource pools / VM Resource allocation

[SiCaNR]

Hi,

I got a question regarding resource pools.

Let say i have 3 resource pools. (High, normal and low) the so called Tug in War model.

A “High” resource pool will have no initial reservation and unlimited/expandable RAM and CPU settings. CPU and Memory shares will be set to high. This resource pool will be devoted for mission-critical VMs.

A second “Normal” resource pool will have no initial reservation and unlimited/expandable RAM and CPU settings. CPU and Memory shares will be set to normal. Normal priority service VMs will be placed into that resource pool and the shares guarantee that VMs in this resource pool do not have priority over mission critical VMs.

A third “Low” resource pool will have no initial reservation and unlimited/expandable RAM and CPU settings. CPU and Memory shares will be set to low. Low priority service VMs, development, and non critical VMs will be placed into this resource pool and the shares guarantee that VMs in this resource pool do not have priority over normal or high VMs.

Now what happens if i see CPU or Memory shares on a specific VM.

For example:

VM X is located in resource pool LOW.

On the VM X i set on the resource location tab the RAM and CPU's to HIGH shares and keep reservation on 0 and unlimited.

What does this specific VM inherit? What kind of shares will it use?

Thanks in advance!

[RvdNieuwendijk]

Remember that shares will only be used when there is a shortage on a resource. So if you have CPU shares and the ESX host has plenty of unused CPU time shares will not be effective. If you have three resource pools High, Normal and Low with CPU shares 5000, 3000 and 2000 it means that in case there is not enough CPU capacity on the host the VM's in the High resource pool together will get 50% of the CPU resources of the ESX host. The VM's in the Normal resource pool together will get 30% of the CPU resources of the ESX host. And the VM's in the Low resource pool will together get 20% of the CPU resources of the ESX host. If all the VM's in a resource pool have the same shares, they will all get the same percentage of CPU time. For instance if you have 10 VM's in the High resource pool each VM will get 5% of CPU time (50%/10). If you have only 2 VM's in the Low resource pool, each VM will get 10% of CPU time (20%/2). So you have to define the share numbers carefully and compare them with the number of VM's in a resource pool.

I hope this makes it clear.

Regards, Robert

[SiCaNR]

Hi Robert,

Thanks for your answer. I'm aware of the fact that resource pools only work when the resources are low.

My question was what happens if i set individual shares on specific VM's.

I was wondering what happens then.

[RvdNieuwendijk]

If you set shares on individual VM's the VM's wil get a percentage of the percentage of the resource pool according to the shares. So in my previous example, if you have two VM's in the low resource pool, VMA with 4000 shares and VMB with 1000 shares, VMA wil get 20%80%=16% and VMB gets 20%20%=4%.

[MattG]

Pg 41 of Resource Mgmt guide:

When adding a VM to a RP:

• If the virtual machine has custom shares assigned, the share value is maintained.

-MattG

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