Hi,
The difference between the numbers here is that supported by the Fabric-1 module and the Fabric-2 modules, for example the N7K-C7010-FAB-1 and N7K-C7010-FAB-2.
The Fabric-1 Module provides 46Gbps per fabric module per slot for a maximum of 230Gbps if using the maximum of five fabric modules. The Fabric-2 Module provides 110Gbps per fabric module per slot for a maximum of 550Gbps when using five fabric modules.
The way the 15TB capacity you're referring to is calculated assumes Fabric-2 modules and is as follows:
(550Gbps/slot) * (16 I/O module slots) = 8800Gbps
plus
(275Gbps/Supervisor Engine slot) * (2 SE module slots) = 550Gbps
Therefore we have (8800Gbps + 550Gbps) * (2 for full duplex operation) = 18.7Tbps
The above is for the 18-slot Nexus 7018. In a Nexus 7010 you only get half that capacity as there's only 8 slots available for I/O modules, so:
(550Gbps/slot) * (8 I/O module slots) = 4400Gbps
plus
(275Gbps/SE slot) * (2 SE module slots) = 550Gbps
So for the Nexus 7010 we have (4400Gbps + 550Gbps) * (2 for full duplex operation) = 9.9Tbps
Note that the Supervisor engine slots only have half the number of channels on the Fabric module as the I/O module slots, and hence half the capacity for the two SE slots.
This is what Cisco are quoting in their Nexus 7000 Series Switches data sheet.
A scalable, fully distributed fabric architecture composed of up to five fabric modules combined with the chassis midplane delivers up to 550 Gbps per slot for 8.8 Tbps, 9.9 Tbps, and 18.7 Tbps of forwarding capacity in the 9-slot, 10-slot, and 18-slot switches, respectively.
These numbers are obviously for the Fabric-2 modules. If you're using Fabric-1 modules then the maximum capacity would be 7.8Tbps in the 18-slot chassis and 4.1Tbps in the 10-slot chassis.
The important point here though is the amount of capacity per slot, and what each I/O modules requires.
The Nexus 7K currently has four different I/O module families (M1, M2, F1 and F2) that have the following fabric bandwidth requirements.
N7K-M148GS-11 46 Gbps
N7K-M148GS-11L 46 Gbps
N7K-M148GT-11 46 Gbps
N7K-M148GT-11L 46 Gbps
N7K-M108X2-12L 80 Gbps
N7K-M132XP-12 80 Gbps
N7K-M132XP-12L 80 Gbps
N7K-M224XP-23L 230G (FAB1) 240G (FAB2)
N7K-M206FQ-23L 230G (FAB1) 240G (FAB2)
N7K-M202CF-22L 200 Gbps
N7K-F132XP-15 230 Gbps
N7K-F248XP-25 230G (FAB1) 480G (FAB2)
N7K-F248XT-25 230G (FAB1) 480G (FAB2)
For the 48-port M1 series cards e.g., N7K-M148GT-11L, the fabric bandwidth requirement is 46Gbps so this module could in theory work in a system with one I/O module. If you want resilience then you'll obviously need two.
For the higher performance I/O modules you need more Fabric modules if you want to be able to run them at their capacity. The 32-port 10-Gigabit F1 I/O module (N7K-F132XP-15) requires 5 Fabric 1 modules to run at full capacity (5 * 46Gbps = 230Gbps). In the event of a failure of one of the Fabric modules this card can continue to operate, but with a reduced fabric capacity of 184Gbps. If you want to run the F1 I/O module with resilience then you need to use the Fabric 2 modules.
I hope that helps to clear the confusion around the fabric capacity of the Nexus 7000.
Regards
