VMware memory management seems to be a tricky balancing act. With cluster RAM, Resource Pools, VMware's management techniques (TPS, ballooning, host swapping), in-guest RAM utilization, swapping, reservations, shares and limits, there are a lot of variables.

I'm in a situation where clients are using dedicated vSphere cluster resources. However, they are configuring the virtual machines as though they were on physical hardware. In turn, this means a standard VM build may have 4 vCPUs and 16GB or more of RAM. I come from the school of starting small (1 vCPU, minimal RAM), checking real-world use and adjusting up as necessary.

Some examples from a "problem" cluster.

Resource pool summary - Looks almost 4:1 overcommitted. Note the high amount of ballooned RAM.

Resource allocation - The Worst Case Allocation column shows that these VMs would have access to less than 50% of their configured RAM under constrained conditions.

The real-time memory utilization graph of the top VM in the listing above. 4 vCPU and 64GB RAM allocated. It averages under 9GB use.

Summary of the same VM

• What are the downsides of overcommitting and overconfiguring resources (specifically RAM) in vSphere environments?
• Assuming that the VMs can run in less RAM, is it fair to say that there's overhead to configuring virtual machines with more RAM than they need?
• What is the counter-argument to: "if a VM has 16GB of RAM allocated, but only uses 4GB, what's the problem??"? E.g. do customers need to be educated?
• What specific metric should be used to meter RAM usage. Tracking the peaks of "Active" versus time?