[Beowulf] Infiniband modular switches

[Mark Hahn]

>> so the switch fabric would be a 'leaf' layer with 12 up and
>> 12 down, and a top layer with 24 down, right?  so 3000 nodes
>> means 250 leaves and 125 tops, 9000 total ports so 4500 cables.
>
> The number of switch layers, or tiers, depends on the cluster size and
> the oversubscription. For full non blocking,  2 layer of 24 switches get
> you up to 288 ports switch, and with 36 ports up to 648 ports.

I guess I'm confused.  wouldn't a non-blocking fabric with 288 host ports
be one layer of 24x 24pt switches (12 up, 12 down to hosts), with _half_ 
as many top-level switches (ie, 12 switches with 24 down each)?