Server Fault is a question and answer site for system and network administrators. Join them; it only takes a minute:

Sign up
Here's how it works:
  1. Anybody can ask a question
  2. Anybody can answer
  3. The best answers are voted up and rise to the top

We just did a fresh install of ESXi 5 on a host that was running ESX 4 before. Nothing has changed hardware wise. After the upgrade network performance is much slower. Even copying a big file from one VM to another VM within same virtual switch is slower compared to other hosts that are running ESX 4.

Network cards are auto-negotiating at 1Gbps as were on ESX 4 prior to upgrade. All settings are default and I haven't played with Advanced Settings at all.

Before opening a case with vmware, wanted to know if I am missing something or if others have experienced similar issues and found a fix?

share|improve this question
What are you using for the guest's network adapters (e1000, vmxnet2, vmxnet3)? Did you upgrade the VMWare tools in your guests following the update? – ewwhite Dec 1 '11 at 1:32
good points, why didn't I think of these :). Network type is Flexible. Is that good or should I try other type? I believe the tools are latest, I have to confirm that with my windows administrator for that. – R D Dec 1 '11 at 2:36
Confirmed that tools are latest. – R D Dec 1 '11 at 19:48
up vote 2 down vote accepted

Not sure if following would relate to your network or not, but we have had this issue as well. What turned out to be cause was network adapter load sharing and failover settings. vSwitch for VMs is using 2 network cards spread across multiple switches. We were doing load sharing (outgoing) between them and obviously internally traffic would come through only 1 nic.

After our upgrade to ESX5i we have had slow performance with this setting. We moved one of the NIC as failvoer NIC instead of load sharing and that fixed our issue.

share|improve this answer
We have similar setting in our environment. I will make the changes tonight and report back the findings. Thanks for your answer! – R D Dec 1 '11 at 19:46
This did it! Thanks. 4 times the difference in network copy speed(from one VM to another!) – R D Dec 1 '11 at 22:46

Your Answer


By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.