Re: Switch or Hub

On a very small cluster, the choice of switch or hub makes very little difference (you don't say how
many nodes). A switch will introduce latency into the network that a hub does not, but the switch
may reduce collisions, depending on packet size and transmission rate.
 
Experimenting with various configurations on a 12 node cluster yielded the following results running
the same benchmark. Swapping a switch in place of a hub, 2% improvement (mostly due to reduced
retransmissions/collisions). Swapping a well known brand of network cards (chipset often used on
motherboards) for higher quality network cards, 9% improvement.
 
My advice:
 
Do not use a cheap switch, less RAM, low backplane bandwidth, and more latency make a poor cluster,
you may get better results with a hub. Invest in good network cards that have linux drivers that do not
require the kernel to relocate the packet data memory offset to transfer it to/from the card.
 
If you are building a large professional cluster with a budget of $10,000's get advice from somewhere else,
you should probably be using something like Myrinet and not Ethernet in the first place ( I wish :>).
 
Happy clustering

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