Why are VMs so slow?


  1. Posts : 984
    X
       #1

    Why are VMs so slow?


    I've run Windows 7 in Oracle Virtual Box.
    I've run Windows 10 in VM Ware Workstation Player.

    The host runs fast. It's an i7-7700K.
    The VMs run slow.

    Why?
      My Computer

  2. jimbo45's Avatar
    Posts : 9,058
    Windows / Linux : Arch Linux
       #2

    margrave55 said:
    I've run Windows 7 in Oracle Virtual Box.
    I've run Windows 10 in VM Ware Workstation Player.

    The host runs fast. It's an i7-7700K.
    The VMs run slow.

    Why?
    @margrave55


    Hi there

    could be all sorts of reasons

    usually these are the main causes :

    1) Insufficient RAM allocated to the Guest OS
    2) VM's allocated on slow HDD's / external devices like USB sticks -- It's OK to allocate a VM on an external SSD connected via USB3-->Sata connector
    3) Incorrect parameters for the Guest OS -- e.g insufficient CPU processors etc .. It's usually best to leave this as default or set to same number of cores / processors in the Host system.
    4) How much concurrent activity is on the HOST while running the VM
    5) How much activity on the VM.
    6) How do you access the VM -- via direct logon to the HOST or via remote application like RDP (or equivalent if on Linux system)
    7) Networking parameters set up incorrectly. E.G virtual Network controller running at half duplex instead of full duplex.
    8) Hardware acceleration not enabled for the GUEST OS. Note sometimes 3D performance can degrade a VM so unless you need 3D performance enhancements on a VM just disable it - keep the hardware acceleration though if its available. - Counter intuitive I know -- reminds me of last time in London going to a mainline Railway terminal to be greeted with a notice "Due to Improvements --Your journey will be considerably delayed !!!!" -- Only in England !!

    9) sufficient video RAM / correct video parameters fir Guest OS.


    That should be enough to go on with -- on a decent machine these days you should be able to get almost native performance out of a VM if it's set up properly.

    Without more detail of what you are doing it's impossible to say -- however if you work down that checklist you should be able to find the bottle necks.

    If the Host runs reasonably fast the chances are it's your RAM/ I/O devices are the culprit. Choose also decent VHD formats for your Guest OS's and don't allocate the entire block in one go -- most VM programs allow you to allocate the max. size and then it will increment say in 2 GB chunks when it needs more space. Use SCSI or SATA for the Virtual I/O controller when setting up the Virtual Hard disks (can be done in Create Virtual Machine wizard).

    Ensure also for VMware type VM's you install vmware tools on the Guest at first boot or for Virtual box install the Virtual box additions.

    Cheers
    jimbo
      My Computer

  3. Bree's Avatar
    Posts : 15,326
    10 Home x64 (2004) (10 Pro on 2nd pc)
       #3

    margrave55 said:
    I've run Windows 7 in Oracle Virtual Box.
    I've run Windows 10 in VM Ware Workstation Player.
    The host runs fast. It's an i7-7700K.

    The VMs run slow.
    Why?
    I've run VMs in Hyper-V. Of the list Jimbo45 gave you I'd put his 'number 2' reason head and shoulders above the rest. Having just switched from an i7 with the VMs stored on its internal HDD to one with an internal SSD I can assure you the change is dramatic. All my VMs now feel like they are running natively on the hardware rather than as a VM.
      My Computers


 

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