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4 port trunk not delivering full bandwidth (HP 2824 - 2848)

Occasional Contributor

4 port trunk not delivering full bandwidth (HP 2824 - 2848)

Hey guys,

Without getting into detail of the application, I am in need for 4 gig connection from switch to switch.

For some reason (which hopefully someone can explain) it seems that when I set up a 4 port trunk, my throughput through the trunk is only using 3/4 lines, and seems to be keeping the 4th for redundancy. If I unplug one of the active ports, the other jumps up and happily handles the traffic for me.

This is not what I want. I want all guns a'blazin.

I am able to get my 4 gig trunk if I team up 5 ports, (the 5th one now appears to be doing the redundancy), so I know it's not a throughput issue with the switches, they can handle that traffic.

I'm using a 2824 and a 2848, but I've also experienced the same problem with two 6108s.

Is there anyway for me to get FULL throughput from a 4 port trunk, without having to resort to a 5 port trunk?

In my lab, I'm using CAT6 for my trunk lines so I can get away with the 5 port solution, but in the real world, I will only have 4 fibres (and only 4 GBIC on the switches).

I've tried standard trunking, and LACP. Both show the same behavior (leaving at least 1 port of the trunk group to act as a fail-over, instead of just giving me all the bandwidth).

My bandwidth testing is using IOMeter, using 4 clients, each with their own gig NIC, blasting to a centralized server that has 4 gig NICs installed. With a 5 port trunk, 4 pipes are saturated, giving me aprox. 440 MB/sec throughput. I need to get this speed with the 4 port trunk, but as it is, if I use 4 ports, only 3 saturate, leaving me with only 320 MB/sec (or so).

Firmware is up to date.

Please help. Any suggestions will be appreciated.
Matt Hobbs
Honored Contributor

Re: 4 port trunk not delivering full bandwidth (HP 2824 - 2848)

Since it does the load balancing randomly with SA/DA mac-address pairs, it's not always equal - in this case though it's bit strange since it seems to be better with a 5 port trunk.

My only suggestion now would be to add more mac-addresses (more clients) into your test to see if that helps.
Occasional Contributor

Re: 4 port trunk not delivering full bandwidth (HP 2824 - 2848)

Thanks for the suggestion.

Tried it, no dice. Still appears that the 4th port is acting as a failover, instead of participating in the load balancing.

Again, if I add a 5th port to the trunk, then the 4 ports (nearly) completely saturate.

With all 4 ports hot, I get 440 MB/sec, or so, which is just shy of actual theoretical gig limits (125MB/sec x 4 = 500 MB/sec).

Any other help is appreciated.