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I have some issue with memory allocation on my Hyper-V 2012 R2 server. Server has 16GB of RAM, with 2 x 12 core CPUs. When I run Get-VMHostNumaNode, I am getting following results:

NodeId                 : 0
ProcessorsAvailability : {0, 0, 0, 0...}
MemoryAvailable        : 6479
MemoryTotal            : 8003
ComputerName           : SRV

NodeId                 : 1
ProcessorsAvailability : {0, 0, 0, 0...}
MemoryAvailable        : 6632
MemoryTotal            : 8192
ComputerName           : SRV

This shows that available memory for both NUMA nodes is 13.1 GB (of 16GB total). OS should take some memory for itself but there is to big 3GB of memory difference.

On the other hand, when I check free memory in servers task manager it show that 15.5 GB is free.

If I try to run VMs on server, maximum memory that can be allocated is around 13GB. I can run 1, 2, 3 or more always same result maximum 13GB of memory combined.

Any suggestions what it can be or in what direction I should search?

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This shows that both NUMA nodes allocated 13.1 GB of memory of 16GB. OS should take some memory for itself but there is to big 3GB of memory difference.

Not quite. It shows 8003Mb available on Node 0 and 8192Mb available on Node 1, which is different to "allocated". Also to note:

6479/8003 = 0.80957
6632/8192 = 0.80957

Coincidence? I think not. It would appear that the memory permitted to be in use by Hyper-V is limited to ~80% of your installed RAM.

On that note, 24 cores and only 16GB of RAM? That's a mightly odd configuration you've got there.

  • Yes you are right, it is 13.1 GB available for NUMA Regarding ~80% - I did not do any special configuration of server. Any idea where I could look for this limitation? And for last configuration is odd but we had to make that configuration, long story, not particularly interesting – Ivan ho ho ho Jan 26 '16 at 13:11
  • I'm afraid I don't know enough about Hyper-V to be able to answer that I'm afraid! – Mark Henderson Jan 26 '16 at 13:29

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