I was looking at the Force 10 S4810P. It supports 48 SFP+ ports and 4 QSFP+ ports. I was wondering if I could plug my SANs to the QSFP+ ports via QDR Infiniband and the rest of my servers to the SFP+ ports via regular Cat6 copper.
I understand that Infiniband data transmission is completely different from ethernet but I was wondering since it runs on QSFP+.
Ethernet and Infiniband are two completely different protocols. If you want to mix the two then you need a gateway device that handles it from the likes of Mellanox. There's no cheap solution to plug Infiniband in to Ethernet.
Yea and yes. QSFP+ is the physical layer, so anything certified to work with the spec should work with those cards. (Please don't take offense) I would suggest though that you need to speak to someone to help you out with this, as this is fairly basic stuff and if you're not careful you're going to end up with a very costly mistake (both financially and reputation wise with your customers).
You would do well to contact Arista Networks and have a chat about their product lineup. Their hardware and feature list is superior, as a company they only do switching and you'll find their pricing competitive.