Tuesday, 15 November 2011

Slow network performance on ESXi hosts with link aggregation

I was getting really slow network throughput from all VMs on a 4GB LAG using ESXi 5.0.0 with the IP hash load balancing policy. 250MB file was taking 20 minutes!! This was with a Dell PowerConnect 5524 in a two switch stack. The LAG was configured correctly.

PowerConnect(Conf)#interface gi1/0/1-2,gi2/0/1-2
PowerConnect(Conf-if)# spanning-tree portfast
PowerConnect(Conf-if)# channel-group 1 mode on
PowerConnect(Conf-if)# exit
PowerConnect#copy running-config startup-conf

The LAG was up as this command showed.
PowerConnect#sh interface status po1

We tested the connection between the VM and my laptop using iperf 

From the VM we ran:
c:\>iperf -s

From my laptop:
c:\>iperf -c 172.x.x.x -i5 -t120 -w1492k

The throughput was not acceptable, giving approx 600Kbps

We broke the stack by pulling power out on the bottom switch and reran the iperf. As you can see things where great again.

Turns out you can't use HDMI 1.3 cables for the stack uplink. It must be HDMI 1.4 which supports EtherLink 

The moral of the story is don't use cheap HDMI cables. Thanks to Mike for is input diagnosing this.

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