Poor performance Hyper-V

twhlgeezer
twhlgeezer used Ask the Experts™
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We are suddenly experiencing very poor performance on some Hyper-V VMs.
Dell 2950, (2x) Xeon 3Ghz, 6x SATA drives 16G memory Server 2008R2..
All was fine until last week.  Now the vms (several XP, one CentOS) are very uniformly slow to respond, and I can not track down the issue.  No changes in vms for quite a while.  Hyper-V monitor reports very normal (low) cpu use by vms.  Performance monitor on host machine show low cpu/network/disk use, 43% committed bytes in use.  In other words, nothing really unusual and the same stats as always.  The only thing that may be differnt is that I did snapshot a machine last week, have done that many times before without issue.

Even just logging in on an XP vm that has been running nicely for a long time is problematic.

Suggestions on where to look next?

Thanks,
Bill
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Top Expert 2012
Commented:
Have you tried rebooting? I had  the same issue troubleshooted but never got a root cause I ended up rebooting which fix the slowness issue.

Commented:
Disable all of the TCP Offload (ToE) settings on the host NIC. This will cause about 20 - 30 seconds of downtime until the NIC is active again so you may want to notify your users or schedule this fix. Another thing I do religously to my Win 2008 servers to increase performace issue like this is disabling Windows scaling on the NIC. You do this by doing the following:

C:\> netsh interface tcp set global autotuninglevel=disabled

By doing these two thing, it will increase the performance of your VM host & VM servers/clients.

Author

Commented:
Thanks will give both a shot this evening after everyone has gone home.  Actually, I did reboot the machine over the weekend, but will do it again just to cover all the bases.

R/
Bill
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Author

Commented:
Moved one semi- busy VM from machine "B" to Machine "A" and rebooted.  Noted no better response from any VM on either hardware box.  Reluctant to make changes in Broadcom before my manager approves.  However did note that the card was set to "First come first served", although it has always been that way and can't see how that could suddenly cause performance degradation.  WIll make nic changes when I get the OK from above.
Top Expert 2012

Commented:
Next I would go with disabling these features on the network card these settings within the VM and physical NIC these settings have fixed my issues on multiple Hyper-v servers.

Make sure you go into the VM disable any Large Send Offload as well
Network Engineer
Commented:
Hyper-V snapshots are known to cause performance degradation, like up to 50%. I would look to merging your snapshot back to the main VHD file. This doesn't seem like a network problem. How is your free disk space? Any events on the host?

Author

Commented:
Thanks again.  Been distracted by other issues the past couple of days.  I cleaned up some old snapshots before moving the VM from "B" to "A", didn't make any difference.  I had one SEL log file problem on the host, but cleared it and restarted, no change in VMs.  Will be adding a switch to the network Sat AM, so will make the NIC changes suggested by wantabe2 then.

Author

Commented:
Not really any perfect solutions, but finally got the linux VM improved by updating.

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