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Why do PING sensors show astronomical or negative request times when PRTG runs on Hyper-V?

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When I run PRTG on a virtual machine on a MS Hyper-V hypervisor I get nonsense PING times (negative or too high). What's going on?

hyper-v negative ping prtg sensor virtual-servers virtualization vm

Created on Feb 2, 2010 1:45:37 PM by  Dirk Paessler [Founder Paessler AG] (10,869) 3 4

Last change on Apr 26, 2011 11:41:48 AM by  Daniel Zobel [Paessler Support]



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Known issue that shows up when Windows Server 2003 is virtualized under Microsoft Hyper-V when a multi-core CPU is assigned to it

We have received reports from customers about PING sensors that show very high (ten thousand milliseconds or more) or even negative request times. The reason for this behavior can be a known issue of Hyper-V that shows up when Windows Server 2003 is virtualized under Microsoft Hyper-V when a multi-core CPU is assigned to it.

The reason for this behavior can be a known issue that shows up when Windows Server 2003 is virtualized under Microsoft Hyper-V when a multi-core CPU is assigned to it. Hyper-V only guarantees “correct timings” for high resolution timers (which we use to measure PING times in PRTG) for single-CPU virtual machines. When using multiple processors, they can actually have slightly different timers. As such, if an application relies on these timers, measured time differences can actually result in negative or astronomical values, seeing as the timers themselves have no fixed common base.

Possible Solutions:

  • Microsoft recommends to use the “/usepmtimer” flag in the boot.ini of the respective guest OS in order to avoid these issues and ensure a correct time measurement.
  • Assign a single core CPU to the virtual machine
  • Migrate to VMware, et al.

For further reference please see http://blogs.msdn.com/tvoellm/archive/2008/06/05/negative-ping-times-in-windows-vm-s-whats-up.aspx

See Also

Created on Feb 2, 2010 1:46:27 PM by  Dirk Paessler [Founder Paessler AG] (10,869) 3 4

Last change on Apr 26, 2011 11:40:04 AM by  Daniel Zobel [Paessler Support]



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Disclaimer: The information in the Paessler Knowledge Base comes without warranty of any kind. Use at your own risk. Before applying any instructions please exercise proper system administrator housekeeping. You must make sure that a proper backup of all your data is available.