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  • 1.  Physical machine vs. Virtual Machine Time

    Broadcom Employee
    Posted Jul 09, 2012 03:58 PM

    In Physical Machines time is taken by the machine from CMOS Battery but in case of Virtual Machine that time is taken by the machine from where?



  • 2.  RE: Physical machine vs. Virtual Machine Time

    Posted Jul 09, 2012 04:02 PM

    Depends on how you have it set up....

    In most cases, since we're talking about servers, there will be local NTP servers on the domain giving the same time to all servers (physical and virtual) so that it doesn't matter. You can set the VM's to use the host server's time settings (where NTP servers can also be set).

    I would set up a local (or a few local if the environment is large enough) servers to act as local NTP servers, pulling from regional NTP servers (pool.ntp.org). In this way only a few servers go out to the internet for time information, and then they provide it to all servers, and desktops, on the internal network... IMO, pretty basic stuff and most often already configured.



  • 3.  RE: Physical machine vs. Virtual Machine Time

    Broadcom Employee
    Posted Jul 09, 2012 04:11 PM

    if it is not connected to internet as well as to the local domain and as well not synchronizing any time from the host then from where it will get the time.



  • 4.  RE: Physical machine vs. Virtual Machine Time

    Posted Jul 09, 2012 04:13 PM

    The VM will be given time byt he host when it boots, and then keep time on its own.



  • 5.  RE: Physical machine vs. Virtual Machine Time

    Posted Jul 09, 2012 04:49 PM

    Ranjna Aggarwal wrote:

    In Physical Machines time is taken by the machine from CMOS Battery but in case of Virtual Machine that time is taken by the machine from where?

    The CMOS battery provides power, not time.  The CMOS clock provides time.

    In a virtual machine, there is a virtual CMOS clock.  However, there is no virtual CMOS battery to keep the virtual CMOS clock running when the virtual machine is powered off.  So, when the virtual CMOS clock is updated, the difference between the virtual machine time and UTC (determined from host time) is stored in the virtual machine's nvram file.  This difference is used to initialize the virtual CMOS clock from the current host time when the virtual machine is next powered on.



  • 6.  RE: Physical machine vs. Virtual Machine Time

    Posted Jul 10, 2012 03:28 AM

    I think this document might have the information you're looking for.

    Tick Tick Tick Tick.

    http://www.vmware.com/files/pdf/Timekeeping-In-VirtualMachines.pdf