Q: What problems might occur if you set a VMware vSphere VM memory limit?

A: In vSphere, it's possible to set memory limits that define a maximum quantity of memory a VM is allowed to consume. You might want to set such limits to protect physical memory from being over-consumed by a memory-hungry VM.

However, if you don't plan carefully, setting a VM memory limit can have an unexpected impact on VM performance. That impact occurs because the VM is unaware that a limit has been placed upon it. A limited VM with 4GB of assigned vRAM operates under the assumption that it has its full memory assignment. As it attempts to use more memory than its limit, that memory must come from ballooning or swapping. Either of these actions can incur a performance tax on the host, which can impact the performance of other VMs on that host.

It's generally not a good idea to set memory limits on VMs. Instead, you should adjust downward the quantity of vRAM assigned to that VM.