Tuesday, April 15, 2014

Long network lost during vMotion

We have observed strange behavior of vMotion during vSphere Design Verification tests after successful vSphere Implementation. By the way that's the reason why Design Verification tests are very important before putting infrastructure into production.But back to the problem. When VM was migrated between ESXi hosts leveraging VMware vMotion we have seen long network lost of VM networking somewhere between 5 and 20 seconds. That's really strange because usually you didn't observe any network lost or maximally lost of single ping from VM perspective.

My first question to implementation team was if  virtual switch option "Notify Switch" is enabled as is documented in vSphere design. The importance of this option is relatively deeply explained for example here and here. The answer from implementation team was positive so problem has to be somewhere else and most probably on physical switches. The main reason of option "Notify Switch" is to quickly update physical switch mac-address-table (aka CAM) and help physical switch to understand on which physical port VM vNIC is connected. So as another potential culprit was intended physical switch. In our case it was  virtual stack of two HP blade modules 6125XLG.

At the end it has been proven by implementation team that HP switch was the culprit. Here is very important HP switch global configuration setting to eliminate this issue.

 mac-address mac-move fast-update  

I didn't find any similar blog post or KB article about this issue so I hope it will be helpful for VMware community. 

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