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So, I'm playing with a couple of QLogic QLA2340s connected directly together. I've got options here to either have them act as a loop, or in point to point mode.

What's the difference if I'm only going to have two machines connected together? Is point-to-point more efficient? The firmware has an option to prefer loop, then fall back to p2p.

Anyone have any idea if there are performance benefits or drawbacks? It's pretty hard to find that information.

[edit] It also turns out my borrowed fiber cable has a break on one of the channels, so I can't actually do real-world tests to figure out which is better. Not until I find someone who's willing to split the shipping from the cheap-cables website.

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1 Answer 1

Point-to-point is the most self-explanatory, and the usual way of connecting just two devices together so they can communicate.

Loop-mode is a way of building a fibre-channel network without using an FC switch. It's analogous to a token-ring network, in that each device in the network forms part of a ring, or loop. I've never seen it used though - the only multi-node FC networks I've worked with have been fully switched, which are more flexible, but more expensive.

Realistically, you're not going to see much difference in performance between loop and p2p with two devices. Personally, I'd stick to p2p, just because it's simpler.

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Why am I not going to see much of a difference? I'm being a bit of a dick here, but I'm really curious. I may just read the spec on it and report back. From the logical arm-chair theorist side, because P2P doesn't need addressing, it ought to be faster (less overhead). I'm just not sure that I'm right is all. –  RandomInsano Jun 10 '12 at 6:16
    
You probably won't see a difference, because they're just two different protocols that ultimately are doing the same thing: passing data between two nodes. The overhead that loop will add compared to the outright bandwidth you have should be minimal. –  growse Jun 10 '12 at 10:49

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