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I have migrated three servers from physical to guest using windows 2008 r2 with hyper-v.

1)Host: DELL R720 with Win 08 r2 enterprise edition

2)Guest: windows 2008 r2 standard edition

I used dedicated NIC (Intel Gigabit 4p I350-T Adapter) for guest OS. But when I ping from guest OS to other any physical servers, the time will appear >1ms randomly ( the normal should be <1ms).

But if i ping from physical to physical servers, it will be <1ms. enter image description here

I try the below method, but the result is the same

  • update the NIC drivers and windows update to the latest

  • Disable the offload on NIC.

  • Changing the cable and network switch

Any suggestion?

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What is the number of processors on the guest? –  Greg Askew Jul 2 '12 at 15:48
    
Assign one only! –  e0594cn Jul 3 '12 at 1:39
    
I'm trying to think of a reason to only have a single processor for a vm. Can't think of one. –  Greg Askew Jul 3 '12 at 2:44
    
What i mean is I select 1 for setting: Number of logical processors.Thanks. –  e0594cn Jul 3 '12 at 5:45

1 Answer 1

Keeping precise time in virtual machines is near impossible due to the nature of the technology used. The hypervisor is going to stretch and compress timer interrupt intervals at its discretion so deviations even out on the large scale. The varying latency reported by ping is likely to be the result of timing problems.

Further reading: http://www.vmware.com/files/pdf/Timekeeping-In-VirtualMachines.pdf (yes, it's VMWare, but the concepts apply for all current Hypervisors)

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@e0594cn At a second glance I've seen that your latencies are often in the region of 10 ms - a magnitude only cumbersomely explained by timer deviations. Have you tried pinging your virtual host from the Hyper-V host itself or vice-versa? –  the-wabbit Jul 2 '12 at 15:57
    
+1. This is not a network issue at all, it is simple a timer deviation issue which is all toop common on virutalization. I run a system like that (financia ltrading) and we had to take it off virtualization because the latency discrepancies were not good to the logging and triggered tons of alarms. –  TomTom Jul 2 '12 at 17:01
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Also, try turning off Processor Power Management on the host. That could be exacerbating the issues. –  Bigbio2002 Jul 2 '12 at 18:39
    
First ,thanks for the answer! The result is the same if I ping Hyper-v Host to the Guests. If i copy few GBs file from other physical sever to VM, the time from ping command will become higher. –  e0594cn Jul 3 '12 at 1:40
    
Any other comment? Is it really a common issue on hyper-v? –  e0594cn Jul 3 '12 at 13:40

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