WS2019 Core Hyper V Memory Utilization

TJ 21 Reputation points
2020-08-18T04:13:26.937+00:00

Running WS 2019 Core:

64GB of Memory

4 Virtual Machines - all memory is using static memory (no dynamic memory allocations)

Machine A: 32 GB
Machine B: 8 GB
Machine C: 8 GB
Machine D: 4 GB

Total = 52 GB

2019 Core PS> Get-Counter '\Memory\Available MBytes' = 6785

The largest I can make a new machine - call it Machine E - is 2 GB else I get an out of memory error.

From reading https://learn.microsoft.com/en-us/windows-server/get-started-19/sys-reqs-19 ... implies that 2 GB is more than enough for WS2019 core.

So, in theory - I should be able to make Machine E 10 GB - but it is limited to 2 GB - else I get an out of memory error on startup. Can someone help me with why the additional 7 or 8 GB cannot be used for another machine?

Windows Server 2019
Windows Server 2019
A Microsoft server operating system that supports enterprise-level management updated to data storage.
3,458 questions
Hyper-V
Hyper-V
A Windows technology providing a hypervisor-based virtualization solution enabling customers to consolidate workloads onto a single server.
2,538 questions
0 comments
Accepted answer
  1. Ian Xue (Shanghai Wicresoft Co., Ltd.) 29,651 Reputation points Microsoft Vendor
    2020-08-18T07:23:04.493+00:00

    Hi,

    The Hyper-V host reserves memory to run Hyper-V. If you want to check the memory available to VMs, you'd use the performance monitor counter Hyper-V Dynamic Memory Balancer\Available Memory.

    Notes:
    The instance name is "System Balancer."
    The Hyper-V Dynamic Memory Balancer\Available Memory value depends on the amount of memory that's used by the application installed in the Hyper-V host, and the amount that's used by vmwp.exe.

    18216-2020-08-18-151323.png

    18149-2020-08-18-152007.png

    You may refer to this link
    https://support2.microsoft.com/en-us/help/2962295/virtual-machine-that-s-running-on-windows-server-2012-r2-doesn-t-start

    Best Regards,
    Ian

    ----------

    Please remember to "Accept Answer" and upvote if the reply is helpful.

    1 person found this answer helpful.
    0 comments

1 additional answer

Sort by: Most helpful
Most helpful Newest Oldest
  1. TJ 21 Reputation points
    2020-08-18T12:36:44.45+00:00

    Thanks Ian. I did find this: https://aidanfinn.com/?p=19043 which pointed to the KB article as well - and gave some additional insight. Finn's post gives a rough rule of thumb (in a table) for a "Host Reserve" which I could not find further documentation on in the KB or anywhere else. So, in my situation:

    64 GB Physical
    57 GB Usable for VM
    7 GB WS 2019 Core + Unusable host reserve held by Core/HyperV

    and...

    Get-Counter '\Hyper-V Dynamic Memory Balancer(*)\Available Memory' is the PS command to see how much you have to build your next VM.

    Again, thanks for the response.

    Are you aware of a document that discusses this Host Reserve and has further information on it - maybe how to minimize it and increase density on a machine that uses static memory allocations?

    0 comments