After teaching vCenter Operations Analyze & Predict and facilitating private workshops with customers I have had this one question that always pops up. What is the criteria for vC Ops to say a VM is oversized or undersized.
To understand how it is calculated is just one thing. What is more important is what you do with the sizing recommendation. Even though Operations may find a machine to be oversized it does not necessarily make it true.
First thing you will need to do is go into “configuration” from the vC Ops website. Here you can configure the thresholds for oversized and undersized VM’s. The settings in the screenshot is right now at default. I have made some marks in the screenshot. “1. Oversized threshold: 1%“, “2 CPU deman less than: 30%“, “3 Memory deman less than: 30%“
What this means is that if a virtual machines is using less than 30%CPU or 30%Memory for 1% of its running time it is considered oversized. Actually it is not based on time. But it is based on “Area” Look at the next screenshot. The threshold of 30% is the “U” and the threshold of 1% is the blue area. So if the area of the blue is more than 1% of the graph it will be considered oversized.
With the default settings of 30% CPU/Memory and oversized threshold of 1% I bet you are going to have A LOT of virtual machines that are considered oversized. For instance if you have some machines who are idling most of the time but in peaks need LOTS of CPU they will definitely be considered oversized even though from the administrator perspective it is not.
I would change the settings for the threshold. Per default you get way too many oversized virtual machines. I recommend the following:
- Oversized Threshold: 10%
- CPU Demand less than: 15%
- Memory Demand less than: 15%
With these settings a virtual machine is oversized if the area on the graph below the threshold “U” (15% CPU/MEM) is 10% or higher. This is just one recommendation, you can tweak the setting to your own liking.
Frank, i know this is kind of an old post. But i’ve been trying to figure out what to do with Oversized VMs Memory recommendation.. We’ve been getting recommended memory values that make no sense, for example, recommending less than 100 MB to a Win2008 server, wich makes.. no sense at all. I take it the vCops is using the Active memory metric for this results (average of it maybe?) And i dont believe its taking peaks into consideration.
Is there any way to make this recommendations a bit more realistic? or at least perhaps add the OS minimum memory requirement to the recommendation?
Because its hard to tell a client “nevermind those values, just put something a bit higher” ha!
Thank you for your time, and great post! the area % is interesting.