[Beowulf] building Infiniband 4x cluster questions

[Hearns, John]

> 
> hi John,
> 
> I had read already about subnet manager but i don't really understand
> this, except when it's only configuration tool.
> 
> I assume it's not something that's critical in terms of bandwidth, it
> doesn't need nonstop bandwidth from the machine & switch is it?
> 

It is critical.

I perhaps am not explaining this correctly.
In an Ethernet network you have a MAC address and the process of ARPing
-
ie if you want to open a connection to another host on the Ethernet,
you broadcast its IP address and you get returned a MAC address.
Hey, that's why its called an ETHERnet (geddit? Oh, the drollery of
those Xerox engineers)

Anyway, on an Infiniband network the Subnet Manager assigns new hosts a
LID (local identifier)
and keeps track of routing tables between them.
No SM, no new hosts join the network.

An Infiniband expert will be along in a minute and explain that you can
operate a fabric without an SM
and I shall stand corrected.



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