When talking about VMware virtualization bottlenecks, 9 out of 10 customers answer their number one bottleneck is memory. Notice how I said bottleneck, not problem. This relates to capacity planning or trying to understand and right size the environment so you can gauge when you need to order more physical infrastructure. Their number one problem is storage, which is quite a different story altogether and I won’t be covering storage in this article (this time). Since memory is such a common point of discussion with my customers, I thought I would dig a little deeper on this topic and share some information around utilization and what it all means.
My customers typically track their utilization in the most common area of vSphere that one might expect to find this information, the DRS Resource Distribution graph at the cluster level.
From the image displayed above, one might think that I am close to memory capacity and I should look at ordering more hardware for my cluster. While in a general sense that might not be a bad idea to begin planning for growth, but let’s take a closer look at what we are seeing. Notice the blue informational icon and how it’s telling us that the displayed information is based on memory consumption. Let’s do a mouse over on the chart that’s being displayed to get some more granular information and what this means.
You can see in the above image that my Virtual Center VM is “Consuming” ~4GB of memory, but in all reality the active memory being used is sitting at ~700MB. DRS entitlement is a measurement that calculates what the load or demand is on the vSphere host/cluster over time, and then projects an average entitlement number for planning purposes. You can use the DRS entitlement numbers as a general planning/forecasting number, but to be honest you still have some capacity within the cluster.
Now I wouldn’t be doing my job if I didn’t make you aware of an easier way to track this information by using software rather than brain power. For those of you that haven’t seen Capacity IQ yet, I would highly encourage you to evaluate the product. Capacity IQ was built for this specific reason, to help you understand when you will need to start thinking about more hardware. It can also help you run your environment more efficiently. There are some great reports that help you identify which virtual machines are not using the resources that were allocated to them. Take them back!
Coming from a VMware system engineer end user position, I can tell you that as your environment begins to grow, capacity management and planning becomes critical. I evaluated Capacity IQ when I was still on the customer side, and did a write up if you are interested in my thoughts on the product.