[Beowulf] 10gig CX4 switches

[Patrick Geoffray]

Greg,

Greg Lindahl wrote:
> I see that HP has a 6-port switch for ~ $4k, too small.

Don't know if it was specific to the model we tested, but hardware flow
control does not work in one direction, even when turned on.

> Arastra looks nice, except that their inexpensive 10base-CR only does
> SFP+, not X2. And CX4 SFP+ doesn't even seem to exist (lack of space
> for the connector?)

There are 3 silicon vendors for small (< 24 ports) integrated 10G 
crossbars: Fujitsu, Fulcrum and Broadcom. They work ok, some better than 
others. Do a N->1 flow-control test (N >= 6) to see which one does not 
have enough internal buffering.

Arastra switches are good, based on Fulcrum. SFP+ Twinax cables are as 
cheap as CX4 and much smaller footprint on the switch, that's why 
everybody is using it today (and QSFP for low-cost fiber). I have seen 
SFP+ to CX4 adapters, but I can't seem to find a source online. You may 
want to ask Arastra. Another solution would be to use SR fiber 
transceivers on both sides, one X2 and one SFP+. That would be a shame 
if you don't need the distance, as it will be significantly more 
expensive than a copper SFP+/CX4 solution.

Patrick