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Hardware-reserved RAM in Windows Server 8 Hyper-V Virtual Machine

    Question

  • I have recently checked memory allocation in a Windows Server 8 DP OS that I have installed using Windows 8 DP Hyper-V. I was stunned to have noticed that 1 MB of RAM in this virtual machine is hardware-reserved. In none of my other VMs equipped with various OSs is there specific hardware reserve RAM allocation. Moreover, Windows Server 2008 R2 installed in a Windows 8 DP Hyper-V virtual machine would not exist longer than 10 minutes after reboot when specifically denied access to PCI firmware settings (via BCD).

    I might be obnoxiously stupid but I would very much like to know what does this 1 MB allocation imply and infer, especially since the hardware RAM allocation size in the parent OS is only 3 MB.

    (BTW, the Building Windows 8 blog article regarding minimum Hyper-V for Windows 8 requiurements mentions 4 GB as the minimum amount of RAM. My parent OS (Windows 8 Client DP) has only 3 GB physical RAM and Hyper-V functions perfectly fine. I experience no problems with simultaneous launch of 2 virtual machines while watching high-resolution movies in a parent OS and snapping desktop and Metro back and forth. So to hell all the talk that Hyper-V is incompatible with low-latency applications. My computer says it is compatible and I have no grounds not to believe my computer. Virtual machines are connected to the Internet and to each other via a single network bridged to a wireless adapter and my VCMs exhibit better network connectivity than my other physical computer that uses cable. So to hell all the talk that of 6 months ago in Technet manuals that you are not supposed to use wireless in Hyper-V and that there should be separate external and internal networks for VMs. My computer tells me a different story, and I have no grounf\ds not to believe my computer. When I initially bought it from an awfcul manufacturer named ASUS with an awful preinstalled Windows 7 Home Basic it had 250 MB hardware allocation and the system was suffering. Now it has only 3 MB thanks to itself, to the Windows 8 developers and to myself. And it blossoms!)


    Vladimir Shipitsyn

    Sunday, February 12, 2012 12:46 PM

All replies

  • I don't know anything about the reserved RAM yet, but as for the low
    latency and RAM requirements, the Hyper-V in Windows 8 is a new version
    and cannot really be held to the requirements of the older version.
     
     

    Bob Comer - Microsoft MVP Virtual Machine
    Sunday, February 12, 2012 1:53 PM
  • I believe (I have way to definitely verify it yet) the hardware-reserved memory allocation in Windows Server 8 VM refers to physical computer's hardware and is provided for the VM to be capable of dynamically configuring its own pci settings to be able to prevent its potential demise in case it might lose or be deprived of an access to resources dynamically configured for it by the hypervisor.

    In a test performed by myself on a Windows Server 2008 R2 VM I have introduced a value of 0 for the bootloader's usefirmwarepcisettings variable. The system was neither able to properly configure its own pci settings nor regain those provided by Hyper-V. Its existence became limited to the amount of time enough tro jam its RAM up to the maximum (max 10 minutes). It could  not be replicated into another VM since Hyper-V provides for only one set of firmware pci resources, namely Intel virtual chip. I have not tried similar test with Windows Server 8 VM but 1 mb hardware RAM reservation gives me hope that the results would be much less disastrous for Windows Server 8 guest OS


    Vladimir Shipitsyn

    Monday, February 13, 2012 1:15 PM