Q. What are the requirements for hot add and remove of memory in Windows Server 2016 Hyper-V?
A. Hot add and remove of memory, officially known as Runtime Memory Resize, is a new feature of Windows Server 2016 Hyper-V. While dynamic memory has been present since Windows Server 2012 the hot add/remove is different as dynamic memory monitors the memory used in a guest then adds/removes based on that usage. This dynamic changing of memory while very useful is not suitable for some scenarios, such as a hoster where constantly changing memory is challenging both for billing and resource planning. With hot add/remove a VM can have its memory resource changed to a specific value without requiring a restart of the guest OS. This would also be useful for many desktop scenarios.
The requirements to use hot add and remove are as follows:
- The guest must be running Windows 10 or Windows Server 2016.. This is because of changes to the kernel mode memory manager to enable memory to be removed (unplugged) or added (plugged) from an operating system that is not present pre-Windows 10/2016. Certain distributions of Linux also support hot-add of memory (but not remove
- Dynamic memory is not used for the VM
- Can be a Generation 1 or Generation 2 VM
- vNUMA is still supported with hot add/remove which is not the case when dynamic memory is used
Note that with the Runtime Memory Resize when memory is removed the actual memory seen in the VM will decrease which is different from dynamic memory pre-2016 that would leave the guest always seeing the high watermark of memory ever present in the VM (with the memory removed consumed by a kernel mode balloon device driver).