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PowerConnect 2724 4gbps Trunking
I have a PowerConnect 2724 switch and two servers with Intel quad port gigabit NICs. I would like to be able to transfer large files between the two at 4 gbps. I have configured both NICs for Static Link Aggregation and the switch with two LAGs using 4 ports. When I try to transfer files I can only get 1 gbps speeds. Both servers have large arrays capable of pushing out more than 4gbps. If I transfer files from two computers to a server I can achieve 2 gbps. After looking around it seems this may be a limitation of LAG where each source MAC can only use one port of the LAG.
Am I correct that this is a limitation of LAG? Is there any way I can configure my 2724 to do what I want? Would a switch that can use LACP be able to do what I want? Thanks for your help.
Zitibake
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October 29th, 2008 14:00
Every ethernet switch has its own capabilities for how to split traffic up over multiple links in a LAG. Some will take the source MAC, destination MAC, and hash them, then use the hash to pick which cable the packets should cross. Dell 5324 could only do that until last year's firmware. If you have two servers talking to one server, they may take different cables... or they may take the same cable (it's up to chance: 4 cables, you have a 1-in-4 chance of traffic from both servers taking the same cable). If you have a hundred servers, then the traffic will be split fairly evenly over the LAG.
Other switches look further into the packet, for example looking at source IP, dest IP, source port, dest port, etc. Each "flow" of packets can then be assigned to a cable. So if you have 1000 web requests in one direction, and web replies in the other, then their traffic will be split-up over the multiple cables, even if the flows are all travelling between the same server and firewall.
In your case, it sounds like you have a single file transfer going. You probably have one big "flow" of packets, from one server to the other server: one source MAC, one dest MAC, one source IP, one dest IP, one source port, one dest port. I am not aware of any ethernet switches that would spread such a load over multiple cables within a LAG.