Have this mellanox cx5 100Gbe and I was wondering If I could use it in the server to connect directly 4 machines at 25Gbe each from that single nic.
The server will run TrueNAS, the clients will be windows, would this work?
The cables are a bit pricy… so I would like to have some kind of confirmation that what i’m planning to do is not very stupid.
You have one QSPF cable coming out of the card pigtailing into four connectors on the other side? We run a similar configuration come out of one of our switches that then goes into three Servers and another switch. I cannot say if this is going to work for you as we use all Cisco, Arista, and Brocade stuff here.
The setup should be possible. But see if we can get others to chime in as well.
Normal and supported.
Get the flavor that matches your equipment.
Unfortunately it will only work on network switches. I preface that with it does not work with connectx3 and connectx2 cards.
rly? They work on my router, but I have not tested a direct connection. Now im thinking I need to 
Sorta kinda.
AFAIK, the Q in QSFP28 stands for “quad”, as in 4x 25Gbit. It requires the 100Gbit end to have the smarts to act as a switch though.
Should work fine as a 25Gbit connection though.
That cable is what I will take if I do it.
one QSFP28 to 4x SFP28.
The cards are Mellanox CX5. 100Gbe have some… 100 to 100 was a bit overkill to my use so planned to do 100 to 25 25 25 25 buying some new NICs.
Soo could some how work but for direct connection maybe not possible. hmmmm
You have Mellanox cards that will split? What model? Connectx5 or 6? My layer three switch will do it with 40 gbit ports.
Per community.mellanox dot com/s/question/0D51T00007KpuEI/using-100gbe-to-4x25gbe-breakout-cables-with-connectx5-ex-nics
No the connect x 5 adapters can not split.
But here is the documentation on the switches that can split.
community.mellanox dot com/s/article/mellanox-breakout-cables-40g–gt–4x10g-and-100g–gt–4x25g
no I have a router that will, I have not tested any Mellanox cards.
Same here. That is why I was saying that the setup could work, but I don’t know if it works with the Mellanox cards.