Potential Packet Loss on VMWare running Exchange

VMware’s KB article 2039495 mentions that in VMware ESXi 4.x and 5.x, very high traffic bursts may cause the VMXnet3 driver to start dropping packets in the Guest OS. This has been observed on Windows Server 2008 R2 running Exchange 2010 with a large number of consecutive clients.

What the article doesn’t mention is the configuration used by the customers that are having this issue.  There is also another VMware KB article 1010071 mentions a packet drop issue in the VMware guest known since ESX 3.  The network driver is basically running out of receive buffers, causing the packets between the Virtual switch and the Guest OS driver to be dropped.

VMware’s temporary solution to this problem is to slowly increase both values in the Guest OS.

To reduce Burst Traffic Drops in Windows 2008 R2 Buffer Settings:

1. Go to Start > Control Panel > Device Manager.
2. Right-click on vmxnet3 and select Properties. 
3. Click the Advanced Tab. 
4. Select Small Rx Buffers and increase the value. 
5. Select Rx Ring #1 Size and increase the value.
6. What KB1010071 mentions and KB2039495 doesn’t, is that when jumbo frames are enabled, you might use a second ring, Rx Ring #2 Size.