6248 with Dell 10GbE SFP+ to Dell supplied Intel X520 in R720 with Intel SFP+ and OM2 cable, no Link.

I've got a stack of 3 x PC6248, using the CX4 stacking modules, no issues there. console#show switch Management Standby Preconfig Plugged-in Switch Code SW Status Status Model ID Model ID Status Version --- ---------- --------- ------------- ------------- ------------- ----------- 1 Stack Mbr PCT6248 PCT6248 OK 3.3.4.1 2 Stack Mbr Oper Stby PCT6248 PCT6248 OK 3.3.4.1 3 Mgmt Sw PCT6248 PCT6248 OK 3.3.4.1 I've just added the 10GbE SFP+ expansion module into slot 2 on switch 2, rebooted the stack. With XG3 connected to the Intel X520 in an R720. console#show fiber-ports optical-transceiver Output Input Port Temp Voltage Current Power Power TX LOS Image may be NSFW.
Clik here to view. [Volt] [mA] [dBm] [dBm] Fault ------- ---- ------- ------- ------- ------- ----- --- 2/xg3 35.6 3.271 7.9 -2.091 -2.512 No No 2/xg4 34.8 3.275 7.6 -2.351 -40.000 No Yes The expansion module is running 2 x Dell badged 10GbE SFP+ modules and when connected together (between XG3 and XG4) with the OM2 cable both ports come up at 10Gb console#show stack-port Configured Running Stack Stack Link Link Unit Interface Mode Mode Status Speed (Gb/s) ---- ---------------- ---------- ---------- ------------ ------------ 1 xg1 Stack Stack Link Up 12 1 xg2 Stack Stack Link Up 12 1 xg3 Ethernet Ethernet Link Down Unknown 1 xg4 Ethernet Ethernet Link Down Unknown 2 xg1 Stack Stack Link Up 12 2 xg2 Stack Stack Link Up 12 2 xg3 Ethernet Ethernet Link Up 10 2 xg4 Ethernet Ethernet Link Up 10 3 xg1 Stack Stack Link Up 12 3 xg2 Stack Stack Link Up 12 3 xg3 Ethernet Ethernet Link Down Unknown 3 xg4 Ethernet Ethernet Link Down Unknown Why when XG3 is connected to the Intel X520 does the link not come up? The Intel X520 needs Intel specific SFP+ modules, which is what I have. This has been tested against 1GbE modules in another switch and comes up at 1Gb as expected. The X520 with the OM2 cable between ports comes up too. I've only had a few minutes to try and get this going but in case I'm missing something significant thought I'd post here before doing too much more. The Intel X520 is in a R720 running ESXi 5.5, so slightly limited in what diagnostics can be performed on the Intel end. Latest firmware/BIOS revisions on all the R720 hardware as of 21/02/2014 SFP+'s in the 6248 are FTLX8571D3BCL SFP+'s in the X520 are AFBR-703SDZ-IN2 I've read a couple of posts where fixing the port speed on the switch to 10gig may help the link come up, but not been back in the office to test yet. And it shouldn't be necessary to fix the speeds. Thoughts appreciated. Thanks Chris