Q: How can I tell how much memory Hyper-V will allocate to virtual machines using Dynamic Memory?
A: All Windows OSs have a Member-Available MBytes performance counter, which shows the amount of memory. However, Hyper-V won't allocate all memory to virtual machines (VMs) and actually has a separate amount of memory it allocates to them.
To view the amount of memory that's available to be allocated to VMs look at performance counter Hyper-V Dynamic Memory Balancer-Available Memory. If you have NUMA spanning turned on, you will see a single value, System Balancer. If you have NUMA spanning turned off, you will see different values for each NUMA node. Note the difference in value between the Available Memory for the Dynamic Memory Balancer and the value for the overall system available memory.
With NUMA spanning enabled:
With NUMA spanning disabled: