5324 bandwidth problem with flow control - works on 5224

Hi all,

 

I have a problem with my 5324 switch. When flow control is enabled on a port on which I try to send data, I cannot use the full Gigabit bandwidth. I only achieve something like 50% usage, i.e. 60 MB/s. On both a PowerConnect 5224 (with 2.1.0.0 firmware) and a Foundry Networks EdgeIron 24G, it works fine.

 

A quick sketch of the situation. I have a VLAN to which 4 PCs are connected, using Intel Pro/1000 MT NICs. One PC sends UDP/IP data at high data rates, 60-100 MB/s. The other three PCs receive the data. I want to use flow control on the links because I do not want to lose packets.

 

When just the sender PC is connected, I can send data from it at any data rate I like (up to 115 MB/s easily). When I connect one or more of the receivers, the maximum sending bandwidth goes down to around 60 MB/s, about half the link bandwidth in other words. At first I suspected the receiver side, but the problem even occurs when flow control is off on the receiving machine!

 

I've tried different PCs to the same switch, different NICs in the PCs, no effect. Still have the problem. To make sure it's got nothing to do with my config, I went back to factory defaults and only enabled FC - still doesn't work.

I've tried the same PCs with a PowerConnect 5224 and a Foundry EdgeIron 24G and everything works fine, with flow control and without.

 

I get the impression that there's a bug in the 5324 firmware that makes flow controlled-sending incredibly slow. When I switch flow control off on the sender, I can send at 100% link bandwidth, but a peer only receveives about 60-70%. This again is different on the 5224 - even without FC, I receive (virtually) all data.

Receiving on the 5324 is fine too, with or without FC. When I crank up two senders that each push out about 60 MB/s, I receive 120 MB/s on the receiving side. Fine. The switch hardware seems to be able to keep up, as you'd expect from the specs and as I have come to expect based on my experience with the 5224.

 

Does anyone have a clue? I've run out of ideas. I dare not install the 5224 2.1.0.0 firmware on my 5324 for fear of rendering the device useless; I can assume there are no hardware differences, but I don't know.

Is there anything else I can test? A setting I can change, something with pause frames maybe. All help is greatly appreciated!

 

morsm.