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

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(Conf)#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.