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I am considering different topologies to attempt at improving FTP upload speeds from many devices into one PC with Quad NIC.

Right now we use on the PC (same IP address on all four ports). From the PC we connect two 1Gb Ethernet cables going to one switch, two more going to another switch. There are two more cables that interconnect the two switches, creating a redundant path.

If four uplink ports on each switch are configured with LACP, do you think that this is speediest connection, or can I get a quicker connection by using a different topology? Keep in mind that single IP address is a requirement.

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Are you monitoring the traffic on the switches? Bytes in / out per-port would tell you whether you're seeing load-balancing across your aggregation groups and where any "hot spots" are. – Evan Anderson Jul 3 '09 at 0:30
I don't think in this case you'd ever be able to load balance across more than 2 links. You can't do LACP to 2 different remote switches, so you'd be doing 2 LACP groups and the server would only ever use one of those links at a time. I'd switch to a 3 and 1 and see if win2k3 allows you to bias to the 3 link LACP. Better performance in most situations and the system is still reliable if a single switch fails. – chris Jul 3 '09 at 2:34
@gregc: How are you managing L2 redundancy? Are the clients on lots of different switches or are they split between the 2 switches the server is attached to? Are you using spanning tree? – chris Jul 3 '09 at 14:03
Each client connects thru three hops to the PC. One hop to a Dell PowerConnect 3524, and another hop thru PowerConnect 5424. Each 3524 is connected with one Ethernet cable to first 5424, and with one Ethernet cable to second 5424. – GregC Jul 3 '09 at 15:02
If you're using spanning tree I believe all the traffic will follow one path through your network. You should to LACP between each of the switches, at the very least. – chris Jul 3 '09 at 15:57
up vote 2 down vote accepted

It really depends on the switch vendor and the specifics of the switch.

The switch may have a variety of algorithms to determine which port it will send any given packet with LACP. With extreme networks switches, for instance, it can use the target MAC, the target port, the source tcp port, the source and target MAC, etc. The point is, if you use LACP and your switch uses the target MAC, you won't see any speed improvement at all. I've used LACP and when everything is working properly it is great. I've also seen people chase their tails for weeks trying to make it work reliably.

Have you considered 10gig? It looks like you can get them for pretty short money, depending on how urgently you need to solve the problem.

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Cannot do 10Gig. The system's already installed. Just trying to figure out a way to squeeze out some more perf. – GregC Jul 3 '09 at 15:04

After talking at length to our IT guys, we settled on using single 5424 core switch with a 4-link trunk to the PC. The other 5424 is just sitting there turned off with wires plugged in, ready to come online if the first 5424 fails.

They recommended changing over to a 5448 (price) or two 6224 switches (redundancy). 6224 supports stacking, so it would allow me to intertwine two 6224 switches.

The other problem with two 6224, besides the cost, is the fact that I won't be able to create two-link LAGs to my remote 3524 switches from one of each 6224 switches.

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