[Beowulf] Infiniband modular switches

[Gilad Shainer]

>>> 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)?


Yes, 2 tiers, 1st with 24X24p and the 2nd with 12x24p