VM balloon memory driver

[big_vern]

Hi,

We have 4 HP blades (bl685c) running ESX 3.5 (Also running VC 2.5).

At the moment we are running way below capacity in terms of ESX host CPU and Memory usuage.

We have a few VMs (latest vmware tools installed) where the ballon memory driver is activated. This is shown in the VM performance graphs and appears to be a mirror image of "Memory Granted (average)"

Checking the the ESX host shows we are only using 50% of Memory and less than 20%CPU, so how come the ballon driver is activating.

My understanding is that this only comes into play when there is memory (RAM) contention on the host, and we have not got any...

It only happens on a few VMs at a time and not always on the same VMs

can anyone explain, thanks guys.

[mcowger]

Do you have memory allocations that exceed reservations?

--Matt

[big_vern]

I've checked all the VMs running on the same host as one VM which is ballooning and the reservations add up to 21GB (the Servers have 32GB of RAM), the summary tab for the host (as viewed in VC) shows 15GB is being used.

Matt - can you explain further on the allocations exceeding the reservations - ? I'm sure I'm being thick today.

[LarsLiljeroth]

We saw the same thing... It was the memory for some of our VM's with 1 GB mem, that were limited to a fixed amout ex 512 mb..

So if the VM want to use more than this it is forced to use Balooning.. Just set the memory ressourse to Unlimited and it should be just ok.

[mcowger · Accepted solution]

Make sure that non of your VM are created as like 2GB RAM but a memory limit of 1GB - that will kick in the baloon driver.

--Matt

[big_vern]

Thanks very much guys - that was the cause of the situation - DOH,, sorry I couldn't award you both the correct answer.

[wapiti10]

I have been trying to fully understand the Balloon Driver and this has been a good post. However it is my understanding that the Balloon Driver takes Memory away from a machine that is not using it in times of need.

Therefore in this situation, since the limit is 512 MB of RAM the Balloon driver kicks in to take back the other 512 MB of RAM that was originally allocated but won't be used becasuse of the Limit.

can someone correct me if I am wrong?

thanks

Dallas

[mcowger]

YOu are correct.

--Matt

[mike_laspina]

Hello,

Here is an excellent paper which includes the balloon driver theory of operation.