[Beowulf] Mutiple IB networks in one cluster

Greg Lindahl lindahl at pbm.com
Wed Feb 5 23:49:13 PST 2014

In the usual Clos network, 1/2 of the nodes can make a single call to
the other 1/2 of the nodes. That's what's non-blocking. Nothing else
is. Running any real code, every node talks to more than one other
node, and the network is not non-blocking.

It makes perfect sense in a telephone network. In the real world, a
Clos network is good but not non-blocking.

On Wed, Feb 05, 2014 at 06:31:11PM -0600, Alan Louis Scheinine wrote:
> Clos is non-blocking up to a certain number of completed connections.
> The number of nonblocking connections is typically much less than
> the number of nodes for which the Clos network provides service.
> Anybody can make a telephone call to anybody else, up until the
> maximum number of completed connections is reached.
>> At least that is what Chuck Seitz drove into our heads whenever we said that a Clos was non-blocking. :-)
>> Scott
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