Enable Hot-Add of Memory with Hyper-V

Enable Hot-Add of Memory with Hyper-V

Q: I want to be able to hot-add memory to a Hyper-V virtual machine (VM) but don't want to use Dynamic Memory--is this possible?

A: Typically, the way Dynamic Memory works is you set three values related to memory:

  • Startup RAM: The amount of memory the VM starts with, which can't be changed while the VM is running.
  • Minimum RAM: The lowest amount of memory the VM can be allocated, which can be reduced while the VM is running but not increased.
  • Maximum RAM: The highest amount of memory the VM can be allocated, which can be increased while the VM is running but not decreased.

For example, you might set the Startup RAM to 1024MB, the Minimum RAM to 512MB and the Maximum RAM to 4096MB. This allows the VM to have additional memory added based on the memory requirements of processes running inside the guest OS and the amount of RAM physically available on the host.

Some organizations don't want to use Dynamic Memory but want the ability to hot-add memory if required. The trick is to do the following:

  • Enable Dynamic Memory, but set the Startup RAM, Minimum RAM, and Maximum RAM to the same value, such as 2048MB, which means the amount of memory available to the VM would be fixed.
  • When memory needs to be hot-added, increase the Maximum RAM value, which will allow the VM to use additional memory. When the VM is shutdown, you can then reset the Startup RAM and Minimum RAM values to match the new Maximum RAM value.

Although technically you are using Dynamic Memory, you have complete control of when and how the memory is allocated using this method; you're essentially hot-adding memory manually as needed.

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